Simulator Study of Signs for A Complex Interchange and Complex Interchange Spreadsheet Tool

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APPENDIX A. SIMULATION STUDY

INTRODUCTION

This appendix discusses the procedure used to develop, test, reduce, and analyze the sequence test topics evaluated in the simulator study.

TOPICS FOR TESTING

A list of potential topics was created as a guideline for the types of sign sequences needing evaluations. The initial list included the following items:

• Driver understanding of gore sign down arrow or arrow per lane versus only signing the exit and not the through movement.
• Driver understanding of down arrow per lane versus shared arrow gore sign.
• Driver understanding of advance signs for multilane freeways.
• Driver lane change behavior when encountering lane ends.
• Driver understanding of exit number plaque placement and driver behavior in a sequence of splits and exits. For example, driver comprehension of signage for left lanes that becomes right exits because of a sequence of splits and exits.
• Driver understanding of the 2009 MUTCD left exit standards.⁽¹⁾
• Driver understanding of exit only sign text to provide confirmation of earlier findings that drivers prefer to get out of an option lane.
• How to sign for distant downstream destinations and challenges with exits being out of order relative to destination proximity.
• Is it better to fill an advance single sign with extra navigation information (i.e., more than two destinations) or to spread the information among multiple signs (possibly ground signs)?
• Which sign elements do drivers read in multisign banks? In what order are they read? Is this lane dependent?
• Driver interpretation of multiple separate exit only panels in the same sign bank.
• Are there limits on the number of lanes that can be effectively communicated by diagrammatic signs (i.e., more than four)?
• Driver interpretation of sign information above one lane that pertains to a different lane. This could include driver assumptions about the pairing of signs with lanes rather than exit order.
• Driver interpretation of route ends signs (typically freeway spurs).
• Driver reading and comprehension of signs with complex yellow panels (i.e., including exit distance and speed limit).
• Driver comprehension of what information goes together on signs with complex layouts.
• How do different sign elements and sign layout options affect drivers' expectations of the upcoming interchange geometry?
• How do different sign elements affect drivers' understanding of the interchange navigation and the destination groupings?
• How to sign for three destinations (legs).

This list was later altered, and topics were assigned to a study using photographs, a TTI simulator study, or both. When deciding which topics should be addressed by the contractor survey and which by the TTI survey, researchers first considered the measures of effectiveness. For topics where it was important to determine how quickly a driver would make a lane choice, a simulator study was desired. If it was only important to know what lane drivers would choose, the contractor survey was a more appropriate and less expensive option. Also, if it was important to see signs in a sequence and for the driver to see their spatial placement on the roadway, the simulator study was more appropriate. While the simulator offered driver immersion and driving data, the laboratory study allowed for quick, inexpensive testing of many different SSs. It is important to note that finalizing the topic list was an iterative process with the division of topics between the TTI simulator study and the contractor survey, as well as the elimination and addition of particular topics.

SIMULATOR STUDY PROCEDURE

TTI houses a Realtime Technologies, Inc. desktop simulator that can be operated with one or three screens depending on study requirements (see figure 41). During the study, test signs were introduced in the simulation along freeway roadways to evaluate drivers' real-time response to the signs. The verbal instructions indicated a starting lane and a destination they were to drive toward. There were three types of destinations: exit, through, or a destination not mentioned on the signs. The starting lane and destination were varied between participants for each SS tested. The simulation environments were designed so that the drivers had ample time to reach an instructed 60–70 mi/h speed before viewing the first SS in each sequence. A speed range was given rather than an exact speed to discourage drivers from focusing their attention too much on the speedometer. The verbal instructions are shown in figure 42. For added realism, the roadside environment housed urban buildings spaced back from the roadway to avoid distraction from the signs. There was no additional traffic so that participants could make uninhibited lane changes and avoid inconsistent and possibly immeasurable distractions.

Figure 41. Photo.Example view of simulator.

Before we get started, I'd like to encourage you to ask questions whenever necessary, but other than that, please keep talking to a minimum.

[Practice (Begin reading as world is started)] The driving simulator you are seated in is an interactive simulator, which means the driving scenes you experience react to your steering and pedal inputs to provide a realistic driving experience. During your drive in the simulator, please drive in a normal fashion. You can adjust your pedals at a position that is comfortable for you. You will only be using the accelerator and brake and will not need to use the clutch on the far left. You will also not need to use your tum signal or any of the buttons on the steering wheel, although it will not hurt anything if you use them.

For the practice session, your task is to get comfortable with driving in the simulator. Go ahead and slowly maneuver onto the roadway and accelerate to a speed of 60 to 70 mi/h. Don't worry about driving at an exact speed limit; just do your best to try to stay in that range. How are you doing? Practice switching back and forth from the accelerator to the brake to get comfortable with the pedals. We can adjust the pedals' position if you need to. Also, I'd like you to practice changing lanes. You do not have to worry about other vehicles being in your blind spot.

You will drive 15 short drives similar to what you are driving now. At the beginning of each drive, I will give you a lane to start in and then will also give you a destination I'd like you to drive toward. When I give you the destination, please say the name back to me so that I know that you heard me correctly. Let's practice that now. Please start in the second-from-the-left lane. Your destination is Newport. (Correct the participant if he or she does not move over to the second-from-left lane and say "Newport" back to you.)

(As the participant approaches the first sign) Ahead you will see signs that will help you navigate to your destination. I only want you to make lane changes as necessary, but please make any necessary lane changes as soon as you are certain you will need to make one. After you pass the signs, please continue driving until I ask you to pull over and stop. When I do that, I will ask you some questions about the signs you saw and the lane choices you made.

(Allow them to pass the signs and then make an appropriate lane change.) Please bring the vehicle to a stop. (Keep the simulation going, and ask questions in the participant packet.)

Now we are going to get a little more practice. Please maneuver to the right lane and maintain a speed of 60-70 mi/h. (When they approach the end of the world) Please slowly coast to a stop. [Save Practice file as instructed on participant packet]

[Introduction] The experimental sessions will be just like the practice session you just did Please remember to drive between 60 and 70 mi/h. I will instruct you to start in a particular lane and will give you a destination to drive toward. Please repeat that destination to me. Remember to only make lane changes as necessary, but please make any necessary lane changes as soon as you are certain you will need to make one. I will instruct you when to pull over for the end of the session and then will ask you some questions that you can answer out loud. Do you have any questions? Please let me know if you need to take a break between sessions.

Figure 42. Illustration. Facilitator instructions.

Due to a combination of simulation geometry limitations and study intent, TTI used a variety of methods and interchange geometries to test the SSs. Several topics described in this section tested driver response to advance signs only (i.e., the 1- and 0.5-mi advance signs). After driving past two sets of advance signs, the simulation was stopped before the interchange came into view. With this approach, upcoming roadway geometry was not an influence on driver behavior, and the advance signs could be tested in isolation. This method of testing was sufficient for many topics because effective signing should result in drivers making decisions well before the gore point. Other topics tested driver response to a sequence of signs including advance signs plus gore signs. For these topics, drivers did reach an actual interchange that matched the geometry indicated on the signs.

In a previous version of the work plan, TTI proposed testing some gore signs in isolation without any advance signs. With preliminary testing in the simulator, it was found that sign viewing time in the simulation was shorter than that of the real world at the same speeds and did not give participants sufficient time to safely make a lane choice. As a result, all topics were tested with at least two signs in the sequence.

For each method, the key recorded measures included lane position, lane change, and distance from SB for the lane change. Verbal follow-up questions (e.g., what other lanes could you have been in to reach your destination?) or questions about information on the set of signs pertaining to an alternate destination than assigned were also asked following each drive segment.

STIMULI DEVELOPMENT

The sign stimuli used in this study were developed using SignCAD^® traffic sign design software. Along with the built-in standards tables of the software, TTI researchers used the MUTCD and the Standard Highway Sign Manual design guidelines to ensure the most accurate and consistent sign representations.^(1,48) In several instances, SignCAD^® could not create exactly what researchers desired. As a result, Adobe Photoshop^® was used to finish the design. Finally, in order to appear more realistic and less cartoon-like in the simulator environment, the sign contrast and saturation were adjusted. Within the simulator environment, signs were viewed at the correct proportion to the roadway dimensions.

EXPERIMENTAL DESIGN

Table 1 lists the number of SSs tested and the number of determined testing variations (SL and instructed destination). Due to the high number of test scenarios, a between-subjects experimental plan was designed that divided the participants and the test scenarios into 6 groups with each participant seeing 15 scenarios, as shown in table 21. The scenarios with an asterisk reflect the second time that a group would drive a simulation from the same topic/SS combination. For example, group 1 would see SS A within topic 1 twice—once when starting in lane 1 and being told to exit (1A_E_1) and the other time starting in lane 3 and being told to go through (1A_T_3). Once reordered, these particular scenarios were separated by many other scenarios so that researchers believed a new SS with new destinations would not be required for the second time the same topic was shown.

Table 21. Test scenarios by topic divided into participant groups.

Topic	Group 1	Group 2	Group 3	Group 4	Group 5	Group 6
1	1A_E_1	1A_E_1*	1A_E_2	1A_T_3	1A_T_2	1A_E_2
	1A_T_3*	1A_T_2	1B_E_1	1B_E_2*	1B_E_1	1B_T_2
	1B_E_2	1B_T_3	1B_T_2*	1B_T_3	1C_E_2	1C_E_1*
	1C_T_2	1C_E_2	1C_E_1	1C_T_2	1C_T_3*	1C_T_3
2	2A_2nd_2	2A_1st_2	2A_T_3	2A_T_4	2A_2nd_4	2A_2nd_5
	2B_2nd_5	2B_2nd_4	2B_T_4	2B_T_3	2B_1st_2	2B_2nd_2
	2C_2nd_4	2C_2nd_5	2C_1st_2	2C_2nd_2	2C_T_4	2C_T_3
3	3A_Left_2	3A_Left_3	3A_Right_2	3A_Right_3	3B_Left_2	3B_Left_3
	3B_Right_2	3B_Right_3	3C_Left_2	3C_Left_3	3C_Right_2	3C_Right_3
4	4A_CNV_1	4A_CNV_2	4A_2nd_2	4A_1st_2	4B_CNV_1	4B_CNV_2
	4B_2nd_2	4B_1st_2	4C_CNV_1	4C_CNV_2	4C_2nd_2	4C_1st_2
5	5A_T_4	5A_Oak_1	5A_Leon_3	5A_Leon_3	5A_Oak_1	5A_T_4
	5B_Leon_3	5B_Oak_1	5B_T_4	5B_T_4	5B_Oak_1	5B_Leon_3
6	6A_T_1	6A_T_1	6A_E_1	6A_E_1	6A_E_3	6A_E_3
	6B_E_3	6B_E_3	6B_T_1	6B_T_1	6B_E_1	6B_E_1

*Second time that a group would see a test variation from the same topic/SS combination.

The scenarios in table 21 were reordered to avoid learning effects. The actual experimental order is shown in table 22.

Table 22. Experimental order by participant group.

Experimental Order	Group 1	Group 2	Group 3	Group 4	Group 5	Group 6
1	1A_E_1	2C_2nd_5	5B_T_4	4C_CNV_2	2B_1st_2	1C_T_3
2	6A_T_1	1A_T_2	1B_E_1	1B_T_3	1C_E_2	5A_T_4
3	2A_2nd_2	5A_Oak_1	3C_Left_2	6B_T_1	5B_Oak_1	4B_CNV_2
4	3A_Left_2	6B_E_3	6A_E_1	2C_2nd_2	3C_Right_2	2A_2nd_5
5	1C_T_2	3B_Right_3	2B_T_4	1A_T_3	6A_E_3	1A_E_2
6	4A_CNV_1	1C_E_2	4A_2nd_2	3A_Right_3	1A_T_2	6B_E_1
7	2B_2nd_5	4B_1st_2	1C_E_1	5B_T_4	4B_CNV_1	3B_Left_3
8	5A_T_4	2A_1st_2	2C_1st_2	2B_T_3	2A_2nd_4	4C_1st_2
9	6B_E_3	1B_T_3	3A_Right_2	4A_1st_2	1B_E_1	2B_2nd_2
10	3B_Right_2	6A_T_1	1A_E_2	1C_T_2	6B_E_1	5B_Leon_3
11	1B_E_2	3A_Left_3	4C_CNV_1	3C_Left_3	3B_Left_2	6A_E_3
12	4B_2nd_2	4A_CNV_2	6B_T_1	6A_E_1	5A_Oak_1	1B_T_2
13	2C_2nd_4	1A_E_1	5A_Leon_3	2A_T_4	2C_T_4	3C_Right_3
14	1A_T_3	2B_2nd_4	1B_T_2	1B_E_2	1C_T_3	2C_T_3
15	5B_Leon_3	5B_Oak_1	2A_T_3	5A_Leon_3	4C_2nd_2	1C_E_1

PARTICIPANT RECRUITMENT

Participants were recruited through the existing TTI participant database and by distributed flyers. Possible participants were required to be 18 years of age or older and have a current Texas driver's license. A total of 42 participants were recruited—18 in College Station and 24 in Houston. Researchers used Texas demographics as a guide for participant recruitment to obtain a more accurate sample of the driving population in the test cities. Gender and age of licensed drivers were obtained from 2009 FHWA statistics, as seen in table 23.⁽⁴²⁾ The education breakdown of Texans ages 18 and older was obtained from the U.S. Census Bureau, as seen in table 24.⁽⁴³⁾ These breakdowns were used as guides, with education taking priority followed by age and then gender.

Table 23. Texas licensed drivers by age and gender (2009).⁽⁴²⁾

Age Category	Males (Percent)	Females (Percent)	Total (Percent)
18–25	12	12	12
25–39	30	30	30
40–54	30	30	30
55–64	15	15	15
65–74	8	8	8
75+	5	5	5
Total	100	100	100

Table 24. Texas educational background based on total population 18+ years old.⁽⁴³⁾

Educational Attainment	Males (Percent)	Females (Percent)	Total (Percent)
No high school diploma	22	20	21
High school diploma or equivalent (GED)	27	27	27
Some college, no degree	28	31	29
Bachelor's degree or higher	23	22	23
Total	100	100	100

DATABASE ASSEMBLY

Participant Files

The simulator study was conducted using a Realtime Technologies Inc. desktop simulator that is operated with one or three screens. The scenarios that were evaluated generated a *.plt file for each participant. The *.plt files are delimited files that can be imported into different analysis software for conducting analyses. The parameters recorded in the study are described in table 25.

Table 25. Variables collected in the simulator study.

Variable	Description
Time (s)	Time from the start of simulation in seconds.
Acceleration (°)	Depression of the acceleration pedal in degrees.
Brake (N)	Force on the brake pedal in Newtons.
Steer (rad)	Steering wheel turn angle in radians (negative is counter clockwise).
Road distance	Cumulative distance within a tile (starts over at 0 for new tile) in meters. Generally, but not always, a tile is 200 m long.
Velocity (m/s)	Participant speed in meters per second.
Lane number	Participant lane number.
Lane position (m)	Participant position within a lane measured from the center of the lane in meters.
Distance 1 (m)	Distance from vehicle to first SB in meters.
Distance 2 (m)	Distance from vehicle to second SB in meters.
Distance 3 (m)	Distance from vehicle to third SB in meters.
Distance 4 (m)	Distance from vehicle to fourth SB in meters.
Distance 5 (m)	Distance from vehicle to fifth SB in meters.

1 ft = 0.305 m

Follow-Up Questions

Each participant was asked follow-up questions to quantify his or her experience/choice of lane after the simulator study. These questions were different for each topic. Details on the questions and scores for the answers are provided in the following sections. A sketch of the path taken by the participant along the simulation scenario, along with test question variation, SL, and destination were also recorded by researchers. This information for each participant and scenario was typed into a spreadsheet to develop a dataset for further analysis.

Demographic Information

Demographic information such as age and gender were recorded for each participant. Table 26 lists the variables and their possible values. This information was typed into a spreadsheet for use in further analysis.

Table 26. Demographic information collected.

Variable	Possible Value
City	C or H
Participant	1 through 24
Gender	1 = male and 2 = female
Age	Any number
Race/ethnicity	1 = White, 2 = African American, 3 = Asian, 4 = Hispanic, and 5 = Other
How many miles a year do you drive?	1 = < 10,000, 2 = 10,000–15,000, and 3 = > 15,000
Where do you do the majority of your driving?	1 = rural, 2 = city, and 3 = freeways
Current employment	1 = full, 2 = part, 3 = retired, 4 = student, 5 = homemaker, and 6 = other
Highest level of education	1 = some high school, 2 = high school, 3 = some college, 4 = college graduate, 5 = some graduate school, and 6 = graduate degree
How often do you play video games?	1 = never, 2 = 1–2/months, 3 = 1–2/weeks, 4 = < 1 h/day, 5 = > 1 h/day

DATA REDUCTION

The assembled data subsets of participant files, follow-up questions, and demographic information were used to build databases for analysis. The participant file subset was exported, and participant number and topic information was added to develop a database for further analysis.

Lane Change Labeling

Participant position within a lane was one of the variables collected in the simulation study. A lane was assumed to be 11.81 ft wide, and the lane position was measured from the center of the lane, with negative values when the car moved left of the centerline and positive values when it moved right. Lane change maneuvers and their direction in the participant data subsets were identified by reviewing the change in lane-change position values. A change in lane position (greater than 1.7 in absolute value) from negative to positive indicated a lane change to the left, whereas a change from positive to negative indicated a lane change to the right. A lane change was recorded when the center of the vehicle crossed the lane line.

To determine the impacts of each SS for various combinations of SL and destination, each lane change maneuver was labeled. Performance of each SS was evaluated by a combination of proper lane choice, absence of unnecessary lane changes, and greater distance from the interchange where the lane changes were made. Apart from the correct, incorrect, and unnecessary lane change labels, different labels were used to account for the differences among the topics. Table 8 explains all labels used in building the dataset. These lane changes were checked with the sketch on the participant data sheet for accuracy and notes/comments. Figure 17 shows an example of the labels used to code lane changes. In the figure, the lane numbers are shown on the bottom of the graphic. The driver started on the right shoulder and was told to start in lane 1, which required several positioning lane changes (see codes starting with P). If the driver moved into lane 2 (as shown with the green solid line), a code of C was used at that point. In this topic, an incorrect lane change (labeled as IR) occurred when the driver moved from lane 1 to lane 2 after the exit ramp. An unnecessary lane change was noted if the driver moved from lane 1 to lane 3 (see orange dashed line).

DATA ANALYSIS AND FINDINGS

Demographic Information

Table 27 lists the demographic information for the 42 participants.

Table 27. Demographic information for 42 participants.

Characteristics		Number (Percent)
Age groups	18–24 years old	5 (12)
	25–39 years old	14 (33)
	40–54 years old	12 (29)
	55–64 years old	8 (19)
	65–74 years old	3 (7)
Race	White	27 (64)
	African American	1 (2)
	Asian	0 (0)
	Hispanic	11 (26)
	Other	2 (5)
	More than one race	1 (2)
Employment	Full time	26 (62)
	Part time	5 (12)
	Retired	5 (12)
	Student	4 (10)
	Homemaker	1 (2)
	Other	1 (2)
Gender	Male	20 (48)
	Female	22 (52)
Education	Some high school	3 (7)
	High school graduate	10 (24)
	Some college/vocational	15 (36)
	College graduate	10 (24)
	Some graduate school	0 (0)
	Graduate degree	4 (10)
Miles driven per year	< 10,000 mi	6 (14)
	10,000-15,000 mi	16 (38)
	> 15,000 mi	20 (48)
Normal driving conditions	Rural roads	5 (12)
	City streets	20 (48)
	Freeways	8 (19)
	Mixed	9 (21)
Frequency of playing video games	Never	25 (60)
	1–2 times/month	12 (29)
	1–2 times/week	3 (7)
	< 1 h/day	0 (0)
	> 1 h/day	2 (5)

Topic 1

Overview

Topic 1 involved testing the understanding and use of different methods for signs for an option lane. The topic evaluated driver understanding of arrow per lane, down arrow per lane, or signing only the exit and not the through movement. Full sequence of three SBs was used to test the understanding and use of the option lane as well as the distance from the signs that lane changes were made. As shown in figure 18 through figure 20, SS A had arrow-per-lane signs, SS B had down arrow-per-lane through signs, and SS C had no pull through sign.

The geometry for the topic was three lanes at the start that then split, with two lanes exiting to the right and two lanes going straight (see figure 11). Table 28 presents the testing variations used in the study, and figure 43 shows how lane changes were coded.

Findings

Table 9 shows a summary of the number of participants with correct, incorrect, and unnecessary lane changes by test variation for topic 1. Plots showing the location of the lane changes are provided in figure 43. Table 28 summarizes the findings from the questions, which were asked following the driving portion.

Table 28. Topic 1 testing variations.

SL	Instructed Destination
	Goodwell, Marshall, or Jackson (Through)	Reading, Deaning, or Louisburg (Exit)
1	No lane change needed.	Exit destination from lane 1 (1X_E_1). Must change lanes (possibility of unnecessary change to lane 3). Codes: 1A_E_1 1B_E_1 1C_E_1
2	Through destination from lane 2 (1X_T_2). No lane change needed (must decide direction, possibility of unnecessary change to lane 1). Codes: 1A_T_2 1B_T_2 1C_T_2	Exit destination from lane 2 (1X_E_2). No lane change needed (must decide direction). Codes: 1A_E_2 1B_E_2 1C_E_2
3	Through destination from lane 3 (1X_T_3). Must change lanes (possibility of unnecessary change to lane 1). Codes: 1A_T_3 1B_T_3 1C_T_3	No lane change needed.

Note: Shaded cells indicate conditions were not tested.

Figure 43. Illustration. Topic 1 lane change coding.

Observations

Observations for this topic are as follows:

• When starting in the left lane (lane 1) and being told to exit (variation 1X_E_1):
  • All drivers correctly exited. Most drivers did make an unnecessary lane change, moving all the way over to lane 3, when lane 2 would have allowed them to exit.
  • Drivers with SS A made their lane changes around SB I, whereas lane changes of drivers with SS B and C had a few more drivers making their decision between SB I and II (see figure 44).
  • Within the follow-up questions, almost all drivers said they had enough time to make a decision and were fully confident of their choice (93 to 100 percent).


• When starting in the center lane (lane 2) and being told to exit (variation 1X_E_2):
  • All drivers correctly exited; however, most drivers made an unnecessary lane change to use the right-most lane (57 to 93 percent of the participants). Only a few of the drivers did not make any lane change (which was preferred). SS B had the most unnecessary lane changes (93 percent), and SS C had the fewest unnecessary lane changes, with 8 (57 percent) compared to 11 or 13 (79 or 93 percent) participants.
  • Most unnecessary lane changes were made near SB I, which was similar for all SSs (see figure 45).
  • All drivers with SS C correctly identified which other lane would lead to their destination and said they had enough time to make the lane choice; however, not all of them were completely confident of their choice.


• When starting in the center lane (lane 2) and being told to go through (variation 1X_T_2):
  • Most drivers stayed in the through lanes. Only one driver, with SS B, made an incorrect lane change to exit. Most drivers did not make any lane change (which is preferred), and a few drivers (between 21 and 29 percent of the participants) made an unnecessary lane change to use the left-most lane.
  • Most drivers with SS A made their unnecessary lane changes around SB I. Most of the unnecessary lane changes for SS B and SS C were beyond SB II (see figure 46).


• When starting in the right lane (lane 3) and being told to go through (variation 1X_T_3):
  • Most drivers made the needed lane changes to stay in the through lanes. Most of the drivers who made the unnecessary lane changes saw SS A. Two drivers with SS C did not make a lane change (which was incorrect) and exited. Note that the name of the through destination for SS C (Jackson) was not present on any of the signs. These drivers made the incorrect decision very early and never corrected. SS A had the highest proportion (71 percent) of drivers who made an unnecessary lane change to use the left-most lane to stay on the freeway.
  • Most drivers made their unnecessary lane changes around SB I. A few of the drivers with SS B and C corrected their position around SB II (see figure 47).
  • Almost all drivers with SS A were completely confident of their choice and said they had enough time to make the lane choice. SS C, without the pull-through sign, had slightly fewer drivers who were confident (71 versus 93 or 100 percent) with their lane selection.


• Overall, participants who viewed SS C were slightly less confident in their lane choice than those who viewed the other two SSs. Participants viewing SS B had the highest confidence.


• Participants were slightly more likely to recall more of the information on the signs (the names of the through and exit destinations) when viewing SS A, which included all information on a single sign and was repeated three times. Overall, participants frequently could not recall the destination for the through lanes when told to exit or the destination for the exit when told to stay on the freeway (percent correct was between 36 and 86 percent; see table 29). Since they did not expect to need that information, the participants did not attempt to retain the information in their memory.

Figure 44. Graph. Topic 1 lane change location 1X_E_1.

 

Figure 45. Graph. Topic 1 lane change location 1X_E_2.

 

Figure 46. Graph. Topic 1 lane change location 1X_T_2.

 

Figure 47. Graph. Topic 1 lane change location 1X_T_3.

Table 29. Topic 1 scores for follow-up questions.

D	SL	SS	Was Leadville a City on the Sign?	Do you Feel Like you Had Enough Time to Make a Lane Choice?	How Confident Were You That You Picked the Correct Lane (1–10a)?		Where did the Through Lanes Go?	Where did the Exit Lanes Go?	Scenario
			Percent Correct	Percent Yes	Percent with 10	Weighted Averageb	Percent Correctc	Percent Correct
E	1	A	79	100	93	9.4	57	N/A	1A_E_1
		B	57	100	93	9.9	36	N/A	1B_E_1
		C	86	93	100	10.0	N/A	N/A	1C_E_1
	2	A	79	93	79	9.4	50	N/A	1A_E_2
		B	79	100	100	10.0	50	N/A	1B_E_2
		C	64	100	57	9.3	N/A	N/A	1C_E_2
T	2	A	79	100	86	9.2	N/A	86	1A_T_1
		B	100	93	100	10.0	N/A	57	1B_T_1
		C	86	93	64	8.9	N/A	64	1C_T_1
	3	A	71	100	93	9.9	N/A	64	1A_T_2
		B	86	93	100	10.0	N/A	57	1B_T_2
		C	57	86	71	8.4	N/A	57	1C_T_2

D = Destination (E = Exit and T = Through). a Participants were asked to rate 1 through 10, with 10 being the most confident. b Weighted average is the number of participants multiplied by the score provided by the participant divided by the total number of participants who answered the question. c For SS C, the driver would not know where the through lanes were going because the information was not on the sign; therefore, this question was not asked. N/A = Question not asked.

Key Finding

Almost all participants made the correct decision to exit or stay on the freeway; however, many unnecessary lane changes were made with each of the three SSs for those people whose SL was either the far left or the far right. Drivers who started in the center lane and were given a through route destination were less likely to make unnecessary lane changes compared to all other conditions. The interesting finding here is that drivers who started in the center lane and were told to exit moved to the far right lane, which was an unnecessary lane change. However, drivers who started in the center lane and were given the through destination did not move to the far left lane. This may have been due to some reluctance on their part to move into the left lane, which is typically used for high-speed passing.

Topic 2

Overview

Topic 2 studied methods for signs when two interstate exits were within close proximity and where there was a need to use sign for three destinations (two interchanges/exits and the through lanes). Figure 21 through figure 23 show the SSs studied; only 1.5- and 1-mi advance signs were used to test when drivers changed lanes. The far right lane was an exit only lane, with the second to the right lane acting as an optional exit for the first interstate exit and then becoming an exit only lane for the second exit. Due to the complexity of the signs, SS A did not indicate the second exit as an exit only in any manner in the advance signs. As shown in figure 21 through figure 23, SS A had multiple signs with exit only panels, SS B had arrow-per-lane signs, and SS C had diagrammatic signs.

Table 30 presents the testing variations used in the study, and figure 12 shows a graphic of the geometrics for the portion of the rod the participants drove on. The simulation was ended prior to the participants reaching any of the exits. Figure 48 shows how lane changes were coded.

Table 30. Topic 2 testing variations.

Lane No.	Instructed Destination
	Longford/Augusta/ Newport (Through)	Clearwater/Steelville/ Sweetwater (Second Exit)	Hutchinson/Pleasanton/ Henderson (First Exit)
1	No lane change needed.	Must change lanes to lane 4.	Must change lanes to lane 4 (possible unnecessary change to lane 5).
2	No lane change needed.	Second exit destination from lane 2 (2X_2nd_2). Must change lanes to lane 4. Codes: 2A_2nd_2 2B_2nd_2 2C_2nd_2	First exit destination from lane 2 (2X_1st_2). Must change lanes to lane 4 (possible unnecessary—but not incorrect—change to lane 5). Codes: 2A_1st_2 2B_1st_2 2C_1st_2
3	Through destination from lane 3 (2X_T_3). No lane change needed (possible unnecessary lane change to left). Codes: 2A_T_3 2B_T_3 2C_T_3	Must change lanes to lane 4 (possible late lane change to lane 4)	Must change lanes to lane 4 (possible unnecessary change to lane 5).
4	Through destination from lane 4 (2X_T_4). Must move over one lane to left. Codes: 2A_T_4 2B_T_4 2C_T_4	Second exit destination from lane 4 (2X_2nd_4). Must stay in lane (possible lane change to left). Codes: 2A_2nd_4 2B_2nd_4 2C_2nd_4	No lane change needed (possible unnecessary change to lane 5).
5	Must change lanes to lane 3.	Second exit destination from lane 5 (2X_2nd_5). Must change lanes to lane 4 (possible unnecessary change to lane 3). Codes: 2A_2nd_5 2B_2nd_5 2C_2nd_5	No lane change needed.

Note: Shaded cells indicate condition was not tested.

Figure 48. Illustration. Topic 2 lane change coding.

Results

Table 10 shows a summary of the number of participants who made correct, incorrect, unnecessary, or pregore undetermined lane changes by test variation for topic 2. Plots showing the location of the lane changes are provided in figure 49 through figure 54.

Questions asked following the driving portion of this topic were as follows:

• How confident are you that you picked the correct lane (1–10)? (See table 10 for the weighted averages.)
• What about the signs influenced your decision to change lanes or not to change lanes? (Answers are provided verbatim in table 31 through table 33.)
• Why did you change lanes (if they moved out of lane 3)? (Responses are provided in table 34.)

Figure 49. Graph. Topic 2 lane change location 2X_T_3.

 

Figure 50. Graph. Topic 2 lane change location 2X_T_4.

 

Figure 51. Graph. Topic 2 lane change location 2X_1st_2.

 

Figure 52. Graph. Topic 2 lane change location 2X_2nd_2.

 

Figure 53. Graph. Topic 2 lane change location 2X_2nd_4.

 

Figure 54. Graph. Topic 2 lane change location 2X_2nd_5.

 

Table 31. Summary of responses to topic 2 question, "What about the signs influenced your decision to change lanes or not change lanes?"

SS	Starting in Lane 3	Starting in Lane 4
A	Being on the far left sign with no exit (left exit). It indicated if I continued straight, I'd head for Longford. It wasn't an exit only lane, and the Longford sign was all the way to the left like it was a through lane. The arrow. The street signs showed the two right lanes going another direction, and the left and middle lanes going north; including Longford. There was no arrow or exit number telling me to get over. There wasn't anything indicating I needed to change lanes.	Because it clearly stated that it was on the left to go there. Because there were arrows pointing to other destinations other than mine. I don't know. There wasn't anything to tell me to change lanes. I wanted to get in the lane under the sign. Placement on the structure was over on the left. Sign was on far left of the roadway. The other right hand three had potential exits coming up, and Longford appears to have an exit coming far away, second from left lane seems most likely to be a through lane.
B	Three arrows didn't say exit. Because the arrow was pointing to three specific lanes for Augusta. I wanted to be away from where everyone was turning. It was a clear sign. It had three arrows which corresponded to the lanes and the other sign had two arrows, and there were two lanes. The arrows. The three arrows showing the three lanes you could be in. Three solid arrows indicating the left three lanes all pointing towards Augusta.	A lot of exits coming up on right and Augusta needed to be in one of the three left lanes. Because three lanes to Augusta, so I moved over to the first one. First set of signs, I thought I was in the correct lane (second from right). Second set of signs confirmed that I needed to be in one of the three left lanes. Large sign that had three arrows pointing to Augusta. The arrows. There were exit only signs for the other places. Where I was going was the left three lanes.
C	Because the tail that led up to Newport was still in this lane. My lane was going to keep going straight. Only lane I felt confident in; sign was a little mindboggling. Single arrow was a little difficult. Other two cities turning off right but Newport straight ahead. Couldn't tell what lanes disappeared with exits. Showed me that up ahead and two right were the destinations I weren't going to. I'm just a cautious driver and don't want to wait until last minute. The last two lanes went to Newport. Wasn't really clear which lanes were going to Newport.	I saw the arrows for the exits jetting off of the straight arrow, where it said Newport. Looked like two right lanes exited to right before Newport. Showed Newport straight ahead and two cities forking to the right. The arrows. The white arrow looked like the lanes were splitting, but I'm not familiar with that type of sign, so I wasn't sure if it meant they were exits or the lanes were splitting off. The wider arrow saying "Newport" was on the left (with other arrows peeling off to right) and the name "Newport" was on the left. There were lanes being diverted to exits on right hand side.

Note: Observations are for when the participants were told the destination was Longford, Augusta, or Newport (i.e., they were to stay on the freeway).

Table 32. Summary of response to topic 2 question, "What about the signs influenced your decision to change lanes or not to change lanes?"

SS	Observations for When Participants were Told the Destination was Hutchinson, Pleasanton, or Henderson (i.e., First destination)	Observations for When Participants were Told to go to Clearwater, Steelville, or Sweetwater (i.e., Second Destination)
A	Exit was coming up. It had arrows over two of the lanes on the right and I needed to be in one of those. It said "Hutchinson" and gave me an arrow. The arrows directing what lane direction I needed to be in. The bright yellow exit on the sign. There were arrows pointing to two right lanes. There were signs for three locations and the right was for Hutchinson.	Clearwater was in the middle, and the other two locations were on the left or right. I normally like to get over early (closest lane to the right) when I see my street name. I still had a mile to go and at least a minute to make a decision. It said Clearwater 1 mile, and I assumed since it was over middle lane I should be in that lane. The furthest sign to the right indicated the two right lanes—the sign for Clearwater was over the center lane. The two right lanes were both exit lanes to Longford, even though I know the second from the right was not an exit only, and I still had 1 mile to go. When I saw the Clearwater 1 1/2 mile I knew to move, but should have been over one more lane to the left.
B	Because they said the exit was coming up. There was a division on the signs. I could tell it was to the far right, stayed in the second lane to make sure before I got over to extreme right. Obvious that Pleasanton was one of two right-most lanes. Sign said 1 mile to Pleasanton and exit arrows pointed to right. The "exit only." The arrows. The immediacy of the exit.	As I got closer, I could tell that I was in the wrong lane based on the arrows in the sign. Because I saw the right sign with Steelville to the right. Because it showed to the right going to Steelville and Pleasanton, they were going towards the same direction. First sign encouraged me to move over because that lane went someplace else; the second sign reassured me that I should be another lane to the right. I needed to get over because my exit was more to the right. The left three lanes were all going straight. Where it said to exit for Steelville—sign itself.
C	Henderson was shown on the right hand side. It showed the exit to Henderson were in the two for right-hand lanes. It was a right exit for Henderson, so I figured I needed to be closer to the right. Lower right arrow pointing to closest exit, Henderson. The arrow curving to the right. The first was a little confusing; needed to read a bunch of names quickly; but Henderson said 1 mile, so I figured I'd better get over to the right fast. Wide arrow, looked like two lanes going to Henderson, figured right two lanes would take me to the connect exit.	Because the directions of the arrows and it showing me which lane would be turning into Sweetwater. Because you had two exits before Sweetwater, or so it looked like to me. I knew I was in the wrong lane and would need to get over to the right and it showed two lanes would be exiting. I know it's a right hand exit because arrow goes to right, but I couldn't tell what lane I needed to be in now to make that exit. The arrows. The sign was totally confusing, so I got in a lane where I could go right or straight.

Note: This table covers observations for when the participants started in lane 2.

Table 33. Summary of responses to topic 2 question, "What about the signs influenced your decision to change lanes or not to change lanes?"

SS	Lane 4	Lane 5
A	Because it said it was coming up in 1 mile and I went to the lane that the sign was over. Because the lane I was in was not an exit only. Hutchinson were the two right lanes; Clearwater looked the next exit beyond that. The next exit was an exit only on the right. The two arrows going to Hutchinson, only one was exit only. They were very clear there was still an exit (43) coming up, so I figured I should be in that lane. Two other cities with exits to the left and right; Clearwater was in the middle.	Because Hutchinson was coming up and I didn't want to be in that lane just in case. Because one of the signs showed an exit to the right and Clearwater was straight ahead, so I changed lanes so I wouldn't exit. Exit only sign for Hutchinson. I was in the lane that was exiting somewhere else. The Hutchinson sign had two lanes for exiting (the two far right lanes). The lane that it was positioned above, the initial lane I was in said exit and you can never tell if you will have the choice to exit or be forced; then the next set of signs, Clearwater was over the lane to my left, so I moved there. Was in an exit lane that I wasn't supposed to be in.
B	Because it had a fork to the far right and the lane I was in would go both that way and straight. Because Pleasanton was definitely going to exit before Steelville. Counting the arrows and lanes and seeing I was in the same lane as the destination arrow. Pleasantville was two right lanes, but the second to the right continued. Steelville was the second arrow and the one on the right was exit only. The exit only was over the far right lane and it didn't show anything that made it look like I needed to move. The sign indicated my lane would go to Steelville and the other lanes someplace else.	Said far right was exit only (and not for my destination). Sign had Steelville over the lane. Steelville was not in the right lane or left, but was in the center, along with another. The arrow was a bit stronger in the second from right lane, but the thicker/bigger one, you that's where it's going. The separation arrows, and there was another arrow on the right for a different exit with a yellow exit sign. There was an exit only in the far right lane. There was Augusta which was the other three lanes, and Pleasantville was right, but my lane looked like either Steelville or Pleasantville.
C	Because there was a left exit only and a right exit only. I had an exit coming up before and would probably have an entrance ramp coming in too. It looked like Henderson was first exit on right, then to Sweetwater could go straight or exit from the lane I was in. It told me Sweetwater was in that lane I was in. It was more clear that that lane was going straight ahead and not veering off to the right. Looked like there was an exit before the one I needed; far right lane would go there. The third lane or this lane, unsure; the arrows influenced my decision.	All the arrows—I wasn't sure if Sweetwater was straight or the small arrow pointing right, so I thought I should be in the next lane over to be prepared for what came next. Because the exit for Newport was north as well as Sweetwater and Newport was straight so I assumed I wouldn't be turning. It looked like it might be the second to the right turn. It looked like the thin arrow followed Sweetwater and that was the second lane. The next exit on the right wasn't Sweetwater and I didn't want to get all the way over because that was Newport. The order of the names from left to right. The signage indicated the exit after the first exit would be Sweetwater.

Note: Observations for when the participants were told to go to Clearwater, Steelville, or Sweetwater (i.e., the second destination).

Table 34. Summary of response to topic 2 question, "Why did you change lanes (if they moved out of lane 3)?"

SL	SS	Comment
3	A	Based on signs with Longford being on far left. Because Longford was shown to be in the left two lanes.
3	B	Because I wanted to, and it was still going to the same destination. I am always more comfortable in the middle lane.
3	C	Because I saw Henderson and other city exits where to right, and I preferred to not get caught in the wrong lane. Because the other ones went somewhere else.

Note: Observations for when the participants were told the destination was Longford, Augusta, or Newport (i.e., they were to stay on the freeway).

Observations

Observations for this topic are as follows:

• Some of the participants may not have made necessary lane changes because the simulation stopped before the gore area was reached.


• Observations for when the participants were given the through destination (Longford, Augusta, or Newport) (i.e., the participants were to stay on the freeway; variations 2X_T_3 or 2X_T_4) include the following:
  • In all but one case, the participants made correct lane changes. Several unnecessary lane changes were made by the participants who started in the lane in which they should stay (lane 3, 2X_T_3).
  • When the participants started in lane 4, they were to make at least one lane change to the left. In all cases but one, the participants did make that lane change. In that one case, it is unknown if the participant would have made the lane change because the simulation did not include the actual exit. Therefore, no difference in lane change behavior was seen for the different SSs for this scenario. The location of the lane changes was similar for the different SSs. SS B had no unnecessary lane changes, SS A had six of the seven participants making unnecessary lane changes, and four of the seven participants in SS C made unnecessary lane changes.
  • The participants were slightly more confident with their lane position for SSs A and B.


• Observations for when the participants were told destinations were served by the first exit (Hutchinson, Pleasanton, or Henderson, variation 2X_1st_2) include the following:
  • All of the participants were in the correct position to make the first exit.
  • To make the first exit, participants needed to move from lane 2 to either lanes 4 or 5. If they changed the minimum number of lanes (i.e., to lane 4), then they were coded as C. If the participants made the extra unnecessary lane change to lane 5 (right-most lane), they were coded with an unnecessary lane change (U). Many of the participants did make the additional unnecessary lane change to move into the far right lane of the freeway. A few more participants (five compared to three) made the unnecessary lane change for SS B.


• Observations for when the participants were told destinations were served by the second exit (Clearwater, Steelville, or Sweetwater, variations 2X_2nd _2, 2X_2nd_4, or 2X_2nd_5) include the following:
  • Regardless of the participant's starting lane, all participants were in the correct lane at the end of the simulation for SS B (arrow-per-lane signs). These participants were also confident with their lane choice. On a scale of 0 to 10, most selected 10; those few that did not select 10 were typically in the condition where their starting position (lane 4) was the lane in which they should stay.
  • Participants seeing SS C (diagrammatic signs) had more correct lane positions than those who saw the multiple signs with exit only panels but not as many as for the arrow-per-lane signs.
  • Six of the seven participants (86 percent) who saw SS A had not changed into the correct lane by the end of the simulation.
  • For SS A and variation 2X_2nd_5, all the participants were very confident (10) that they picked the correct lane, although only four of the participants had made the correct lane change from lane 5 to lane 4. A similar finding was observed for when the participants started in lane 4. Most said they were confident in their lane position; however, three made incorrect lane changes.


• The average confidence ratings for SSs A, B, and C were 9.3, 9.7, and 7.7, respectively. The drivers were most confident with their lane choice for the signs that provided an arrow-per-lane (SS B). Drivers were least confident with the diagrammatic sign (SS C).


• When asked why they made their lane choice, most participants mentioned the arrows on the signs regardless of what SS they were presented, although many who viewed SS A also mentioned that the location of the signs above the roadway was an indication of what lane they should be in.


• Participant responses for the topic 2 question on what influenced their lane decisions showed that drivers relied on arrows for navigation. Even when given a through destination, drivers looked at the arrows for the exiting lanes to help them determine which lanes they should not be in rather than using an approach of determining which lane they should be in. A lack of clear arrow guidance could result in unnecessary lane changes by drivers who want to be confident that they are in a lane that goes to their destination. In addition, comments indicated that some drivers knew they still had more time before needing to make a lane choice.


• There was less confidence in the chosen lanes for drivers who viewed the large diagrammatic sign in SS C.

Key Finding

For SS B, which had an arrow-per-lane design, all participants (42) made correct lane change decisions. SS C, which had a diagrammatic sign, also had many correct lane change decisions, with five or more of the seven participants in a group making the correct decision. Of the 42 participants who viewed SS C, only 3 made incorrect lane change decisions. SS A (multiple signs with exit only panels) did not have as favorable results. For example, 6 of the 42 participants made incorrect lane change decisions. SS A also had more of the participants needing additional information to make a lane change decision.

Topic 3

Overview

Topic 3 evaluated signing for an upcoming exit that had a Y-split into two directions. Researchers looked at how quickly drivers made a lane choice and whether one SS separated drivers into their proper lane more effectively for the upcoming Y-split. Signing options included a split sign to explore if it helped to maneuver drivers into the appropriate lane for the Y-split in advance of the initial exit. The SSs are shown in figure 24 through figure 26. SS A had shared exit signs, SS B had split exit signs both in advance and at the gore, and SS C had shared exit advance signs with a split exit sign at the gore. For SSs A and C, at the Y-split, the city exit on top of the sign branched to the left, and the one on the bottom branched to the right. Figure 55 shows a copy of the MUTCD figure that provides an example of signing for a two-lane exit ramp with two dropped lanes and a bifurcation beyond the mainline gore.⁽¹⁾

The geometry presented to the driver was three lanes at the beginning with two lanes exiting to the right (geometry in simulator showed that the exit lanes traveled straight and the through lane curved to the left, as shown in figure 13). Participants had to decide whether to follow the through lane that curved to the left or take the exit. The simulation was stopped prior to the physical splitting of the exit into a left fork and a right fork. The testing variations are shown in table 35. Figure 56 shows how lane changes were coded, and figure 30 shows where the lane change occurred.

Figure 55. Illustration. MUTCD Figure 2E-34: Example of signing for a two-lane exit ramp with two dropped lanes and a bifurcation beyond the mainline gore.⁽¹⁾

 

Table 35. Topic 3 testing variations.

SL	Instructed Destination
	Murray/Richey/ Marsing (Through)	Winner/Edison/Mission (Left Fork)	Groton/Victor/Walker (Right Fork)
1	Not tested.	Not tested.	Not tested.
2	Not tested.	Left fork destination from lane 2 (3X_Left_2). Must remain in lane. Codes: 3A_Left_2 3B_Left_2 3C_Left_2	Right fork destination from lane 2 (3X_Right_2). Must change lanes. Codes: 3A_Right_2 3B_Right_2 3C_Right_2
3	Not tested.	Left fork destination from lane 3 (3X_Left_3). Must change lanes. Codes: 3A_Left_3 3B_Left_3 3C_Left_3	Right fork destination from lane 3 (3X_Right_3). Must remain in lane. Codes: 3A_Right_3 3B_Right_3 3C_Right_3

Note: Shaded cells indicate that the condition was not tested.

Figure 56. Illustration. Topic 3 lane change coding.

Table 11 shows a summary of the number of participants with correct, incorrect, unnecessary, and swerve lane changes by test variation for topic 3. Plots showing the location of the lane changes are provided in figure 30. Questions asked following the driving segment included the following:

• Which lane do you think you need to be in to get to your destination: right, left, or either? (Table 36 lists the percent correct by test variation.)
• Which exit do you think is coming first: Winner/Edison/Mission or Groton/Victor/
  Walker? (Table 37 provides the answers to the question.)
• Do you think Winner/Edison/Mission is on the left or right ahead (if they took the exit)? (Table 38 provides the answers to the question.)
• Do you think Groton/Victor/Walker is on the left or right ahead (if they took the exit)? (Table 39 provides the answers to the question.)

Table 36. Topic 3 question, "Which lane do you think you need to be in to get to your destination: right, left, or either?"

SS	SL	Exit Ramp Lane for Assigned Destination	Incorrect	Correct	Percent Correct
A	2	Left	5	2	29
A	2	Right	6	1	14
A	3	Left	5	2	29
A	3	Right	5	2	29
B	2	Left	0	7	100
B	2	Right	0	7	100
B	3	Left	1	6	86
B	3	Right	2	5	71
C	2	Left	1	6	86
C	2	Right	1	6	86
C	3	Left	2	5	71
C	3	Right	1	6	86

Table 37. Topic 3 question, "Which exit do you think is coming first: Winner/Edison/Mission or Groton/Victor/Walker?"

SS	SL	Assigned Fork	Winner, Edison, Mission	Groton, Victor, Walker	Same	I Do Not Know
A	2	Left	6	0	0	1
A	2	Right	4	2	0	1
A	3	Left	2	3	2	0
A	3	Right	6	0	0	1
B	2	Left	0	6	1	0
B	2	Right	0	5	0	2
B	3	Left	0	2	1	4
B	3	Right	0	4	2	1
C	2	Left	0	4	0	3
C	2	Right	3	2	2	0
C	3	Left	3	3	1	0
C	3	Right	1	3	0	3

 

Table 38. Topic 3 question, "Do you think Winner/Edison/Mission is on the left or right ahead (if the participant took the exit)?"

SS	SL	I Do Not Know	Left	Left/Right	Right
A	2	0	2	1	4
A	3	2	0	0	5
B	2	0	7	0	0
B	3	0	5	0	2
C	2	1	5	0	1
C	3	0	6	0	1

Note: Only participants who were given Winner, Edison, or Mission (i.e., left fork) as their destination were asked this question.

 

Table 39. Topic 3 question, "Do you think Groton/Victor/Walker is on the left or right ahead (if the participant took the exit)?"

SS	SL	I Do Not Know	Left	Left/Right	Right
A	2	2	0	1	4
A	3	1	1	0	5
B	2	0	0	0	7
B	3	0	0	0	7
C	2	0	0	0	7
C*	3	0	0	0	6

*One participant who was assigned the right fork started in lane 3, viewed SS C, and did not take the exit.
Note: Only participants who were given Groton, Victor, or Walker (i.e., right fork) as their destination were asked this question.

Observations

Observations for this topic are as follows:

• When the destination was the left fork (Winner, Edison, or Mission) and drivers started in lane 2 (variation 3X_Left_2), participants should not have moved out of their starting lane. SS C had the fewest participants making an incorrect lane change. SS A with the destinations stacked had the most incorrect lane changes with all of those incorrect lane changes occurring near the initial SB (see figure 27).
• When the destination was the left fork (Winner, Edison, or Mission) and drivers started in lane 3 (variation 3X_Left_3), all of the participants failed to change lanes into the correct lane in advance of the Y-split with SS A (i.e., the participants did not recognize that the stacking of the cities was associated with lane position). Only half of the participants did so with SS C, which had stacked city names for the first two signs and the divided sign on the final SB. For SS C, four of the seven participants correctly changed their lane near the third SB (see figure 28). SS B had the cities split on the initial SB, and five of the seven participants made the correct lane change near this SB, with another participant making the lane change near the second SB. The remaining participant did not make any lane change in response to the signs.
• When the destination was the right fork (Groton, Victor, or Walker) and drivers started in lane 2 (variation 3X_Right_2), the patterns observed for the left fork situation were similar to the right fork situation. Participants made the correct lane change when they saw the sign with the exits side by side rather than stacked. For SS B, this was the initial SB, while for SS C, this was the final SB. Only one of the participants made a correct lane change for SS A (see figure 29).
• When the destination was the right fork (Groton, Victor, or Walker) and drivers started in lane 3 (variation 3X_Right_3), the SS did not matter. All of the participants stayed in their lane (see figure 30).
• When asked after the simulation had stopped which lane they needed to be in prior to the split, participants were least likely to answer the correct lane with SS A and were most likely to pick the correct lane with SS B.
• When asked which side of the road a destination was on, participants most often answered the side that corresponded to the side of the sign containing the name of the destination for SS B and C. If they had viewed SS A, they most often thought both destinations would exit to the right.
• When destinations were stacked on a sign, drivers were more likely to answer that the exit to the top destination would come first and both exits would be to the right. On a split sign, the drivers were more likely to answer that the destination on the right side of the sign would come first and the exit directions would correspond to the side of the sign the destination was on. The participants' unprompted comments, however, indicated mixed assumptions on destination positioning on a sign and what that meant about when and where the exit would be.

Key Finding

The lateral location of the destination on the sign was used by the participants in making a lane change decision. As can be seen in figure 28 and figure 29, several lane changes were made at the first appearance of the split exit sign (at SB I location for SS B and at SB III location for SS C). While several incorrect lane changes were made for each SS, SS B, which used split exit signs at all three SB locations, had the fewest and was judged superior in comparison to the other two arrangements.

Topic 4

Overview

Topic 4 evaluated whether it was better to fill an advance single sign with supplemental way-finding information or to spread the information among multiple signs including, ground-mounted signs. AASHTO Guidelines for the Selection of Supplemental Guide Signs for Traffic Generators Adjacent to Freeways provides a basis for developing State policies for selecting supplemental guide signs for traffic generators adjacent to freeways.⁽⁴⁴⁾ For this topic, gore signs with advance signs at 1 mi were used to explore whether sign spreading on a single bridge or on multiple bridges improved where the lane change was occurring. As shown in figure 31 through figure 33, SS A had a single sign with multiple destinations, SS B had split signs on a single SB, and SS C had sign spreading on multiple SBs. All of the SSs had the exit number panels positioned on the upper right. Table 40 shows the testing variations used in the study, and figure 57 shows how lane changes were coded.

Table 40. Topic 4 testing variations.

SL	Instructed Destination
	Convention Center	Kenston/Wright/Aspen (Second Exit)	Fitch/Martin/Clark (First Exit)
1	Convention center destination from lane 1 (4X_CNV_1). Must change lanes and take exit. Codes: 4A_CNV_1 4B_CNV_1 4C_CNV_1	No lane change needed.	No lane change needed.
2	Convention center destination from lane 2 (4X_CNV_2). Must remain in lane and take exit. Codes: 4A_CNV_2 4B_CNV_2 4C_CNV_2	Second exit destination from lane 2 (4X_2nd_2). Must pass exit and remain in lane. Codes: 4A_2nd_2 4B_2nd_2 4C_2nd_2	First exit destination from lane 2 (4X_1st_2). Must remain in lane and take exit. Codes: 4A_1st_2 4B_1st_2 4C_1st_2

Note: Shaded cells indicate that the condition was not tested.

Note: See table 28 for meaning of codes.
Figure 57. Illustration. Topic 4 lane change coding.

Results

Table 12 shows a summary of the number of participants with correct, incorrect, unnecessary, and indecisive lane changes by test variation for topic 4. Plots showing the location of the lane changes are provided in figure 58 through figure 61. Questions that were asked following the driving segment include the following:

• What lane would you have gotten in to go to Kenston/Wright/Aspen: left or right? (Answers are provided in table 41.)
• Should you have exited if you wanted to go to the convention center? (Answers are provided in table 42.)
• How did you know to exit (if they took the exit)? (Answers are provided in table 43.)
• How much longer do you drive until you will exit (if they did not take the exit)? (Answers are provided in table 44.)

Figure 58. Graph. Topic 4 lane change location 4X_CNV_1.

 

Figure 59. Graph. Topic 4 lane change location 4X_CNV_2.

 

Figure 60. Graph. Topic 4 lane change location 4X_2nd_2.

 

Figure 61. Graph. Topic 4 lane change location 4X_1st_2.

 

Table 41. Topic 4 question, "What lane would you have gotten in to go to Kenston/Wright/Aspen?"

SL	SS	Either	I Do Not Know	Left	Right	Total
1	A	0	1	6	0	7
1	B	0	0	5	2	7
1	C	0	7	0	0	7
2	A	1	1	4	1	7
2	B	1	0	4	2	7
2	C	0	5	1	1	7

Note: Only participants who were given the Convention Center as a destination were asked this question.

Table 42. Topic 4 question, "Should you have exited if you wanted to go to the Convention Center?"

Destination	SS	I Do Not Know	No	Yes	Total
1st	A	0	1	6	7
1st	B	2	4	1	7
1st	C	0	0	7	7
2nd	A	2	3	2	7
2nd	B	2	2	3	7
2nd	C	2	0	5	7

Note: Participants who were instructed to go to the Convention Center were not asked this question. All participants started in lane 2.

 

Table 43. Summary of responses to topic 4 question, "How did you know to exit (if they took the exit)?"

SL	SS A	SS B	SS C
1	Because the sign said convention center under that street. I saw Fitch with Convention Center. I should have gone to right because the first sign said it was an exit to both. Said 5A for convention center on first sign; but didn't say convention center again.	Because the sign said convention center was at 5A. I do not know, sign never said. It said convention center use 5A and that was to Marlin. It said it was exit 5A. Sign said "Convention Center use 5A." The number 5A. Under Convention Center sign said use exit 5A.	5A. Convention Center sign said 5A. Convention Center use exit 5A. Said exit 5A. Sign said it was exit 5A. The sign said convention center use 5A. The sign said to use exit 5A.
2	Feel like I remember convention center being written next to Finch on first sign. Fitch Way and Convention Center were the same exit. Fitch Way sign said Convention Center earlier. It said Fitch Way/ Convention Center on a sign. It said Fitch Way/ Convention Center 1 mile. The first sign had Fitch Way and Convention Center together—assumed same exit.	Because it said Convention Center use exit 5A. Convention center sign said use exit 5A. Sign before last said convention center use 5A. Sign said Convention Center at 5A.	Because mile marker 5A was identified for the Convention Center. Convention center said 5A, went by the numbers. It said exit 5A. Said we exit 5A. Sign said we use exit 5A for Convention Center. The sign said convention center use 5A. The sign told me to use exit 5A.

Table 44. Summary of responses to topic 4 question, "How much longer do you drive until you will exit (if they did not take the exit)?"

Destination	SS A	SS B	SS C
Fitch/Martin/ Clark (first exit)	Saw sign that said Finch Way; no indication of distance.
Convention Center	I missed it, originally said Fitch Way/Convention Center, then didn't see convention center on this part. I do not know, I thought the exit I just passed had been about a mile, but I was expecting more information. I feel like I missed my exit. 0.5 mi or less. About 0.25 mi.	Because I saw sign in middle, it said exit 5A, then when I saw exit 5A, was confused because it said street name, but 5A, so I took it. It will be the next exit. About 0.25 mi.	No responses provided.
Kenston/ Wright/Aspen (second exit)	1.5 mi. 0.5 mi. 2.5 mi. Don't know—1st sign said 1.5 mi, but signs were too far apart, but would rather have them too far apart than too close.	I do not know. 1.5 mi. 0.5 mi. The last sign said 0.5 mi, so I wasn't in the right lane yet.	Don't know—never said. 0.5 mi. About 1 min, 1.5 mi?

Note: Blank cells indicate that the question was not asked because all drivers took the correct exit.

Observations

Observations for this topic are as follows:

• Observations for when the participants were told the destination was the convention center (variation 4X_CNV_1 or 4X_CNV_2) are as follows:
  • Participants viewing SS C (supplemental sign on a separate structure) were always correct in their lane selection regardless of their starting lane.
  • About half of the participants who started in the far left lane missed the exit to the Convention Center with SS A. Only one of the participants who started in lane 2 missed the Convention Center with SS A. This may have been due to the fact that the advance signs for SS A included a multiple-line sign over lane 2, which may have been difficult for those in lane 1 to read quickly from that position.
  • SS B was also associated with participants who missed the exit to the Convention Center. This SS, with the supplemental sign in the center of the SB, also caused several people to incorrectly change lanes to continue through the interchange, suggesting that drivers were aligning themselves with the lateral position of the sign on the bridge.
  • SS B and SS A had similar results, indicating these SSs were not as well understood as the sign spreading approach used with SS C. Because only seven participants saw each SS, additional study should be considered for this topic.
  • When asked what lane they would have gotten in to go to Kenston/Wright/Aspen when their assigned destination was convention center, more participants who viewed SS C did not know compared to those who viewed SS A and SS B. This suggests that drivers may have been scanning the sign arrays for their target destination and when not found, they quickly dismissed the distractor destinations from memory. The majority of the participants viewing SS A and SS B said the left lane, which was incorrect. The drivers would have needed to stay in the right lane for the downstream exit. There was no indication on the sign that the exit was on the left, although the position of the sign on the SB may have led some of the participants to think the exit was to the left. The fact that drivers who saw SSs A and B recalled the distractor destinations may be due to the fact that they appeared on the same SBs as the convention center target destination sign.


• An Observation for when the participants started in lane 2 and were told the destination was Kenston, Wright, or Aspen Avenue (i.e., second exit; variation 4X_2nd_2) include the following:
  • SS B had the most incorrect lane changes with only two of the seven participants correctly staying in their original lane. The spreading of the information on the single SB caused the sign with the information about the second destination (i.e., to Wright Ave) to be over lane 1, which was the lane five of the seven participants entered. When the sign spreading was across multiple SBs or when the information was stacked on one sign, fewer drivers made the incorrect lane change to the left.


• Observations for when the participants started in lane 2 and were told the destination was Fitch, Martin, or Clark Way (i.e., first exit; variation 4X_1st_2) include the following:
  • Almost all of the participants correctly drove these scenarios. Table 42 shows the results for when participants were asked if they should have exited if they had wanted to go to the convention center. Slightly more participants answered yes correctly when they viewed SS C with the standalone guide sign than those who viewed SSs A and B.
  • Table 43 shows that the participants who took the exit said they knew to exit because the Convention Center was mentioned on a sign regardless of the SS they viewed.
  • The question presented in table 44 was asked to indirectly determine if any participants realized they missed their exit. Comments indicated that at least two participants viewing SS A knowingly missed their exit, indicating some uncertainty in the signs.
  • When asked about the second exit, most participants viewing SS C with sign spreading did not know what lane to be in for that exit, as shown in table 41. This may have been because the SS involved a more engaging thought process in determining where they would need to exit. Of those who viewed SSs B and C, the majority of participants answered that they would incorrectly need to be in the left lane for the second exit, showing drivers tended to maneuver to the lane under the sign with their destination.

Key Finding

For most of the variations studied, SS C (sign spreading across two SBs) had the most participants make the correct lane change decision, although SS A (information for next exit stacked on one sign) also had many of the participants correctly making lane positioning decisions. When the destination information was spread across multiple signs on a single bridge, several participants made incorrect lane changes to the left when the instructions were to go to the second destination. These drivers may have been positioning their vehicles into the lane under the sign with their intended destination. This finding indicates that spreading information about the next exit across multiple signs on a single bridge may have unintended consequences if the SB also includes a sign for another exit that is located to the left of the preferred lane.

Topic 5

Overview

Topic 5 evaluated the effectiveness of sign spreading when there were many bits of information on one SB. The question being explored was, "Does sign spreading affect where lane changes occur?" As shown in figure 34 and figure 35, SS A did not have sign spreading, while SS B had sign spreading across many SBs.

Table 45 presents the testing variations used in the study, and figure 62 shows how lane changes were coded. Because only 1.5- and 1-mi advance signs were used in the simulation, there could be some cases where the needed lane change would have occurred after the simulation was stopped. Therefore, the coding included a pregore undetermined option.

Results

Table 13 shows a summary of the number of participants who made correct, incorrect, unnecessary, and swerve lane changes by test variation for topic 5. Plots showing the location of the lane changes are provided in figure 63 through figure 65.

Table 46 provides the percentage of participants who answered 1 or 10 along with the weighted average for each test variation for the three questions asked following the driving portion of the topic.

Table 45. Topic 5 testing variations.

SL	Instructed Destination
	Davenport (Through)	Oak St	Leon
1	Must change to lane 2.	Oak St. destination from lane 1 (5X_Oak_1). Must change to lane 3. Codes: 5A_Oak_1 5B_Oak_1	No lane change needed.
2	No lane change needed.	Must change to lane 3.	Must change to lane 1.
3	No lane change needed.	No lane change needed.	Leon destination from lane 3 (5X_Leon_3). Must change to lane 1. Codes: 5A_Leon_3 5B_Leon_4
4	Through destination from lane 4 (5X_T_4). Must change to lane 3. Codes: 5A_T_4 5B_T_4	Must change to lane 3.	Must change to lane 1.
5	Must change to lane 3.	Must change to lane 3.	Must change to lane 1.

Note: Shaded cells indicate that the condition was not tested.

Note: See table 28 for meaning of codes.

Figure 62. Illustration. Topic 5 lane change coding.

 

Figure 63. Graph. Topic 5 lane change location 5X_T_4.

 

Figure 64. Graph. Topic 5 lane change location 5X_Oak_1.

 

Figure 65. Graph. Topic 5 lane change location 5X_Leon_3.

 

Table 46. Topic 5 responses to questions.

Scenario	How Confident are you that you Picked the Correct Lane? (Scale of 1 to 10 with 10 Being Most Confident)		Was that Too Much Information at One Time? (Scale of 1 to 10 with 1 being an Okay Amount and 10 Being too Much Information)			How Closely Spaced Do you Think the Signs Were? (Scale of 1 to 10, with 1 Being Okay and 10 Being Way too Close)
	Percent with 10	Weighted	Percent with 1	Percent with 10	Weighted	Percent with 1	Percent with 10	Weighted
5A_Leon_3	93	9.4	21	7	4.6	N/A	N/A	N/A
5A_Oak_1	50	8.5	36	7	4.1	N/A	N/A	N/A
5A_T_4	86	9.8	21	7	5.1	N/A	N/A	N/A
5B_Leon_3	86	9.3	N/A	N/A	N/A	29	7	4.1
5B_Oak_1	36	7.7	N/A	N/A	N/A	43	0	3.4
5B_T_4	100	10.0	N/A	N/A	N/A	29	0	3.9

N/A = Question not asked.

Observations

Observations for this topic are as follows:

• Observations for when the participants were told the destination was Davenport (i.e., they were to stay on the freeway; variations 5A_T_4 or 5B_T_4) include the following:
  • SS A had more unnecessary lane changes compared to SS B; half of the participants with SS A had unnecessary lane changes, while SS B had no unnecessary lane changes. Because SS A had more signs on a single SB, the sign for Davenport was farther to the left, which may have resulted in participants trying to position themselves below the Davenport sign, resulting in an unnecessary—but not incorrect—lane change. Because SS B spread the signs across more SBs, the sign for Davenport was closer to the right edge of the freeway compared to the position within SS A (see figure 66 through figure 68). SS B, however, had 4 of the 14 participants make an incorrect straight movement. The drivers should have shifted another lane to the left to avoid being in the two exit-only lanes. These findings indicate that the position on the SB of the pull-through sign is important.
  • Almost all of the participants were confident they were in the correct lane for Davenport.
• Observations for when the participants were told the destination was Oak Street (i.e., they would need to make a downstream exit to the right; variations 5A_Oak_1 or 5B_Oak_1) include the following:
  • Several incorrect lane changes were made with both SSs. Only slightly more than half of the participants for each SS were in the correct lane at the end of the simulation. The location of the lane changes for both SSs was varied (see figure 64).
  • The participants were not as confident that they were in the correct lane for the Oak Street exit compared to the responses for Davenport or Leon; however, the weighted score was still high (7.7 or 8.5).
• Observations for when the participants were told the destination was Leon (i.e., they would need to make a downstream exit to the left; variations 5A_Leon_1 or 5B_Leon_1) include the following:
  • Almost all of the participants correctly drove the simulation with both SSs. Correct position occurred earlier in the simulation for SS A compared to SS B (see figure 65).
  • The participants were very confident they were in the correct lane for Leon (weighted score of 9.4 or 9.3 on a scale of 10).
• All participants were asked their confidence in their lane selection. Participants’ unprompted comments indicated that several gave a low confidence rating because they knew they had not yet maneuvered to the correct lane.
• All participants who viewed SS A were asked about the quantity of information viewed at one time, with 1 being an okay amount and 10 being too much information. Only one participant in each group that saw SS A believed there was way too much information at one time. Most felt it was more toward 1 than 10.
• Participants who viewed SS B were asked how closely spaced they felt the signs were. Generally, the participants did not feel the signs were placed too closely. At most, only one of the participants in a group who saw SS B said the signs were way too closely spaced. Most felt it was more toward 1 than 10.

Note: Notice the position of the Davenport sign.
Figure 66. Screenshot. SS 5-A: no sign spreading.

 

Figure 67. Screenshot. SS 5-B: Initial signs viewed when sign spreading is used.

 

Note: Notice the position of the Davenport sign when sign spreading is used.
Figure 68. Screenshot. SS 5-B: sign spreading across SBs.

Key Finding

The lateral position of a pull-through sign on the SB is important. SS A had more unnecessary lane changes compared to SS B; half of the participants with SS A had unnecessary lane changes, while SS B had no unnecessary lane changes. Because SS A had more signs on a single SB, the sign for Davenport was farther to the left, which may have resulted in participants trying to position themselves below the Davenport sign, causing in an unnecessary—but not incorrect—lane change. SS B had several participants who incorrectly did not move out of their initial lane when told to go to the through destination (Davenport).

Topic 6

Overview

Topic 6 evaluated driver understanding of the 2009 MUTCD left exit standards.⁽¹⁾ Only 1- and 0.5-mi advance signs were used to test how quickly drivers identified the left exit and changed lanes and whether there was confusion on whether it was an exit only or optional exit. As figure 36 and figure 37 show, SS A had a yellow plaque at the top left, and SS B had a yellow panel at the bottom of the sign. Table 47 presents the testing variations used in the study, and figure 69 shows how lane changes were coded.

Table 47 Topic 6 testing variations.

SL	Instructed Destination
	Longmont or Youngstown (Through)	Enterprise or Winnsboro (Exit)
1	Through destination from lane 1 (6X_T_1). No lane change needed (possible unnecessary change to lane 2). Codes: 6A_T_1 6B_T_1	Exit destination from lane 1 (6X_E_1). Must remain in lane to exit. Codes: 6A_E_1 6B_E_1
2	No lane change needed.	Must change to lane 1.
3	No lane change needed.	Exit destination from lane 3 (6X_E_3). Must change to lane 1. Codes: 6A_E_3 6B_E_3
4	No lane change needed.	Must change to lane 1.
5	No lane change needed.	Must change to lane 1.

Note: Shaded cells indicate that the condition was not tested.

Figure 69. Illustration. Topic 6 lane change coding.

Results

Table 14 shows a summary of the number of participants with correct, incorrect, unnecessary, and pregore undetermined lane changes by test variation for topic 6. Plots showing the location of the lane changes are provided in figure 70 through figure 72. Table 48 summarizes the findings from the questions asked following the driving portion.

 

Figure 70. Graph. Topic 6 lane change location 6X_T_1.

 

Figure 71. Graph. Topic 6 lane change location 6X_E_1.

 

Figure 72. Graph. Topic 6 lane change location 6X_E_3.

 

Table 48. Topic 6 scores for follow-up questions.

Destination	SL	SS	Percent Correct for “Is the ramp to Enterprise/Winsborro on the left or the right?”
Through	1	A	85
		B	100
Exit	1	A	100
		B	100
	3	A	100
		B	100

Observations

Observations for this topic are as follows:

• Observations for when participants were told to start in lane 1 and go through (variation 6X_T_1) include the following:
  • All drivers were in position to correctly stay on the freeway. Some drivers did make an unnecessary lane change to avoid being in the left-most lane. The proportion of unnecessary lane changes was slightly higher among drivers with SS B.
  • Drivers with SS B made more unnecessary lane changes just after SB I when compared with drivers of SS A (see figure 70).
  • All drivers with SS B correctly identified the ramp as being on the left, whereas only 85 percent of drivers (12 of 14) with SS A did so.
• Observations for when participants were told to start in lane 1 and exit (variation 6X_E_1) include the following:
  • All drivers were in position to correctly exit. Once they reached lane 1, all of the participants correctly stayed in that lane.
  • All lane changes were made around the same distance from the start point for both SSs.
  • All drivers identified the left exit correctly in the follow-up question.
• Observations for when participants were told to start in lane 3 and exit (variation 6X_E_3) include the following:
  • Most drivers correctly changed lanes to be able to make the left exit; however, one driver in each SS was in the pregore undetermined group.
  • All lane changes were made around the same distance from the start point for both SSs.
  • All drivers identified the left exit correctly in the follow-up question.
• Participants’ unprompted comments implied that some of the participants who moved out of the far left lane may have done so for personal preference rather than because they thought the sign indicated they had to or they would be forced to exit.

Key Finding

Generally, for the two SSs tested under this topic, participants understood which side of the road the exit was located. It is unclear if this was because the participants were cued by the placement of the sign over the left lane, read the word “left” on the signs, or a combination of the two. The placement of the sign over the left lane resulted in participants correctly avoiding traveling across multiple lanes to make a right exit. However, when the participants did not need to make a left exit, they frequently moved out of the left-most lane (even though the lane was not an exit only lane) due to personal preference. A few more of the non-exiting participants seeing SS B with the yellow panel at the bottom of the sign moved out of the left-most lane (8 of 14) compared to the participants seeing SS A with the yellow plaque at the top left (5 of 14). For this study, the difference between these two SSs was minimal.

 

SUMMARY

This appendix discussed the procedure used to develop, test, reduce, and analyze several SSs evaluated in a simulator study. From a list of potential topics identified by the research team as needing evaluation, the following topics were selected for the simulator study:

• Topic 1: Option lane.
• Topic 2: Close proximity of two interstate exits.
• Topic 3: Y-split.
• Topic 4: Information spreading (more signs per bridge).
• Topic 5: Information spreading (multiple SBs).
• Topic 6: Left exit.

During the study, test signs were introduced in the simulation along freeways to evaluate drivers’ real-time response to the signs. The verbal instructions indicated a starting lane and a destination the participants were to drive toward. The key recorded measures included lane position, lane change, and distance from SB for the lane change.

Topic 1 tested the understanding and use of different methods to sign for an option lane. The topic evaluated driver understanding of arrow per lane, down arrow per lane, or signing only the exit and not the through movement. Almost all participants made the correct decision to exit or stay on the freeway; however, many unnecessary lane changes were made with each of the three SSs for those participants whose SL was either the far left or the far right. Drivers who started in the center lane and were given a through route destination were less likely to make unnecessary lane changes compared to all other conditions. The interesting finding is that drivers who started in the center lanes and were told to exit moved to the far right lane, which included an unnecessary lane change. However, drivers who started in the center lane and were given the through destination did not move to the far left lane. This may have been due to some reluctance on their part to move into the left lane, which is typically used for high-speed passing.

Topic 2 studied sign methods when two interstate exits were within close proximity and when a need existed to sign for three destinations (two interchanges/exits and the through lanes). For the SS that had an arrow-per-lane design, all participants (42) made correct lane change decisions. The SS that had a diagrammatic sign also had many correct lane change decisions, with five or more of the seven participants in a group making the correct decision. Of the 42 participants who viewed the diagrammatic sign, only three made incorrect lane-change decisions. The SS with exit only panels did not have as favorable results (e.g., 6 of the 42 participants made incorrect lane change decisions).

Topic 3 evaluated signing for an upcoming exit that had a Y-split into two directions. Signing options included a split sign to determine whether it helped maneuver drivers into the appropriate lane for the Y-split in advance of the initial exit. The split sign showed the two destinations side by side with a vertical white line separation. For SS B, the split sign was used for the two advance signs and at the gore. SS C only used the split sign at the gore with the two advance signs showing the destinations vertically stacked. SS A used the vertical stacked format for both the two advance signs and the gore sign. The data indicated that the lateral location of the destination on the sign was used by the participants in making a lane change decision. Several lane changes were made at the first appearance of the split exit sign (at the first advance sign location for SS B and near the gore sign for SS C). While several incorrect lane changes were made for each SS, the SS that used split signs at all three SB locations had the fewest.

Topic 4 evaluated whether it was better to fill an advance single sign with supplemental way-finding information or to spread the information among multiple signs, including ground-mounted signs. Gore signs with advance signs at 1 mi were used to explore whether sign spreading on a single bridge or on multiple bridges improved where the lane change was occurring. For most of the variations studied, the SS with sign spreading across two SBs had the most participants make the correct lane change decision, although the SS with information for the next exit stacked on one sign also had many of the participants correctly making lane positioning decisions. When the destination information was spread across multiple signs on a single bridge, several participants made incorrect lane changes to the left when the instructions were to go to the second destination. These drivers may have been positioning their vehicles into the lane under the sign with their intended destination. This finding indicates that spreading information about the next exit across multiple signs on a single bridge may have unintended consequences if the SB also includes a sign for another exit that is located to the left of the preferred lane.

Topic 5 evaluated the effectiveness of sign spreading when there were many bits of information on one SB. SS A did not have sign spreading, and SS B had sign spreading across many SBs. The findings indicated that the lateral position of a pull-through sign on the SB is important. SS A had more unnecessary lane changes compared to SS B; half of the participants with SS A had unnecessary lane changes, while SS B had no unnecessary lane changes. Because SS A had more signs on a single SB, the sign for Davenport was farther to the left, which may have resulted in participants trying to position themselves below the Davenport sign, resulting in an unnecessary—but not incorrect—lane change. SS B had several participants who incorrectly did not move out of their initial lane when told to go to the through destination (Davenport).

Topic 6 evaluated driver understanding of the 2009 MUTCD left exit standards.(1) Only 1- and 0.5-mi advance signs were used to test how quickly drivers identified the left exit and changed lanes and if there was confusion on whether it was an exit only or optional exit. SS A had a yellow plaque at the top left, and SS B had a yellow panel at the bottom of the sign. Generally, for the two SSs tested under this topic, participants understood which side of the road the exit was located. It is unclear if this was because the participants were cued by the placement of the sign over the left lane, read the word “left” on the signs, or a combination of the two. The placement of the sign over the left lane resulted in the participants correctly avoiding moving across multiple lanes to make a right exit. However, when the participants did not need to make a left exit, they frequently moved out of the left-most lane (even though the lane was not an exit only lane) due to personal preference. A few more of the non-exiting participants seeing SS B with the yellow panel at the bottom of the sign moved out of the left-most lane (8 of 14) compared to the participants seeing SS A with the yellow plaque at the top left (5 of 14). Overall, for this study, the difference between these two SSs was minimal.