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

PDF files can be viewed with the Acrobat® Reader®

CHAPTER 3. DRIVER SIMULATOR EVALUATION OF SIGN TREATMENTS

This chapter discusses the procedure used to develop, test, reduce, and analyze the sequence test topics evaluated in the simulator study. A list of potential sign sequences needing evaluations was created. This list was then refined to determine which were appropriate for a simulator study. For example, if it was important to determine how quickly a driver would make a lane choice or if it was important to see signs in a sequence and for the driver to see their spatial placement on the roadway, a simulator study was more appropriate., Table 1 provides an overview of the six topics selected for the simulator study and lists the number of SSs tested and the number of determined testing variations (SL and instructed destination).

PROCEDURE

TTI houses a Realtime Technologies, Inc. desktop simulator that can be operated with one or three screens depending on study requirements. During the study, test signs were introduced to the simulation along freeway roadways to evaluate drivers' real-time response to the signs. Drivers were verbally provided with a starting lane and a destination they were to drive toward. The starting lane and destination (exit, through, or a destination not mentioned on the signs) were varied between participants for each SS tested. The simulation environments were designed so that the driver had ample time to reach an instructed 60–70 mi/h speed before viewing the first SS in each sequence.

For each method, the recorded measures included lane choice with proximity to each set of signs, any unnecessary lane changes or indecisiveness, speed, and braking. 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.

EXPERIMENTAL DESIGN

Figure 11 through figure 16 provide the geometry roadway and SB location for each of the six topics. Due to the high number of test scenarios, a between-participants experimental plan was designed that divided the participants and the test scenarios into 6 groups with each participant seeing 15 scenarios. For a few scenarios, a group would see a test variation from the same topic/SS combination. Once reordered, these particular scenarios were separated by many others so that researchers believed a new SS with new destinations would not be required for the second time the same topic was shown.

Figure 11. Illustration. Geometry for topic 1.

 

Figure 12. Illustration. Geometry for topic 2.

 

Figure 13. Illustration. Geometry for topic 3.

 

Figure 14. Illustration. Geometry for topic 4.

 

Figure 15. Illustration. Geometry for topic 5.

 

Figure 16. Illustration. Geometry for topic 6.

PARTICIPANT RECRUITMENT

A total of 42 participants were recruited—18 in College Station, TX, and 24 in Houston, TX. 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.⁽⁴²⁾ The education breakdown of Texans ages 18 and older was obtained from the U.S. Census Bureau.⁽⁴³⁾ These breakdowns were used as guides, with education taking priority followed by age and then gender. The number of participants by education was as follows:

• Some high school: Three participants (7 percent).
• High school graduate: 10 participants (24 percent).
• Some college/vocational: 15 participants (36 percent).
• College graduate: 10 participants (24 percent).
• Some graduate school: Zero participants (0 percent).
• Graduate degree: Four participants (10 percent).

The number of participants by age group was as follows:

• < 24 years old: Three participants (7 percent).
• 24–33 years old: 12 participants (29 percent).
• 34–43 years old: Nine participants (21 percent).
• 44–53 years old: Five participants (12 percent).
• 54–63 years old: 10 participants (24 percent).
• 64–73 years old: Three participants (7 percent).

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 containing the lane position and distant travel data was exported, and participant number and topic information were added to develop a database for further analysis.

Participant position within a lane was one of the variables collected in the simulation study. A lane was assumed to be 11.8 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. Apart from the correct, incorrect, and unnecessary lane change labels, different labels were used to account for the differences among the topics. Figure 17 shows an example of the lane change coding used. Table 8 explains all labels used in building the dataset. These lane changes were checked with the sketch on participant data sheet for accuracy and notes/comments.

Figure 17. Illustration. Example of labels used to code lane changes.

Table 8. Labels used to code lane changes shown in plots.

Label ID	Description
N	Number of participants driving a particular testing variation.
C	Correct lane change.
H	Lane change to be in the lane instructed as the starting lane. This is also the correct lane for the requested through or exit maneuver (in other words, the participant did not need to make an additional lane change to satisfy instructions).
U	Unnecessary lane change.
✓	Sum of C, H, and U.
IL	Incorrect lane change to the left.
IR	Incorrect lane change to the right.
IS	Incorrect lane change to go through.
✗	Sum of IL, IR, and IS.
G	Pregore undetermined. For some scenarios, the simulation was stopped before the driver reached the interchange; therefore, it could not always be determined at that point whether the participant had made a correct or incorrect lane choice.
S	Swerve (swerve from left lane to right and back to left is counted as two).
IC	Lane change to correct an incorrect lane change (other than swerve, typically at a later time).
UC	Lane change to correct an unnecessary lane change (other than swerve, typically at a later time).
W	Representing indecision (i.e., S, IC, or UC).
PS	Lane change to move into the SL.
PE	Lane change to move into the end lane/pulling over to end simulation.
PC	Lane change leading to the correct lane change.
PI	Lane change leading to the incorrect lane change.
PU	Lane change leading to the unnecessary lane change.
L	Last recording for the participant (to estimate/double check PE).
SB I	Sign bridge 1 location.
SB II	Sign bridge 2 location.
SB III	Sign bridge 3 location.
SB IV	Sign bridge 4 location.
SB V	Sign bridge 5 location.

DATA ANALYSIS AND FINDINGS

Topic 1

Overview

Topic 1 involved testing driver understanding and use of the 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. As shown in figure 18 through figure 20, SS 1-A has arrow-per-lane signs, SS 1-B has down arrow-per-lane through signs, and SS 1-C has no pull through signs. 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).

Figure 18. Illustration. SS 1-A: arrow-per-lane sign.⁽¹⁾

 

Figure 19. Illustration. SS 1-B: down arrow-per-lane through sign.⁽¹⁾

 

Figure 20. Illustration. SS 1-C: no pull through sign.⁽¹⁾

Observations

Table 9 shows a summary of the number of participants with correct, incorrect, and unnecessary lane changes by test variation for topic 1. Note that each participant was assigned one of these codes: C, H, U, IL, IR, and IS. If the participant had more than one type of lane change (e.g., both an incorrect lane change to the right (IR) and an unnecessary lane change (U)), the code was assigned in the following priority order: IL, IR, IS, U, C, and H. Observations for topic 1 are as follows:

• When starting in lane 1 and being told to exit (variation 1X_E_1, see figure 17 for explanation of codes), all drivers correctly exited. Most drivers did make an unnecessary lane change. Within the follow-up questions, almost all drivers said they had enough time to make a decision and were confident of their choice (93 to 100 percent).
• When starting in 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 drivers did not make any lane change (which is preferred). SS 1-B had the most unnecessary lane changes (93 percent), and SS 1-C had the fewest unnecessary lane changes (8 compared to 11 or 13 participants).
• When starting in lane 2 and being told to go through (variation 1X_T_2), most drivers stayed on the through lanes. Only one driver with SS 1-B made an incorrect lane change to exit. Most drivers did not make any lane changes (which is preferred), and a few drivers made an unnecessary lane change to use the left-most lane.
• When starting in lane 3 and being told to go through (variation 1X_T_3), most drivers made the needed lane changes to stay on the through lanes. Most drivers who made unnecessary lane changes saw SS 1-A. Two drivers with SS 1-C did not make a lane change (which was incorrect) and exited. Note that the name of the through destination for SS 1-C (Jackson) was not present on any of the signs. These drivers made the incorrect decision very early and never corrected. SS 1-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.
• Overall, participants who viewed SS 1-C were slightly less confident in their lane choice than those who viewed the other two SSs. Participants viewing SS 1-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 1-A, which included all information on a single sign which 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). Since they did not expect to need that information, the participants did not attempt to retain it.

Table 9. Topic 1: number of participants with lane change type by test variation.

SS	D	SL	N	C	H	U	✓	IL	IR	IS	✗	% ✓	% ✗	%U	Scenario
A	E	1	14	5	0	9	14	0	0	0	0	100	0	64	1A_E_1
B			14	5	0	9	14	0	0	0	0	100	0	64	1B_E_1
C			14	6	0	8	14	0	0	0	0	100	0	57	1C_E_1
A		2	14	0	3	11	14	0	0	0	0	100	0	79	1A_E_2
B			14	0	1	13	14	0	0	0	0	100	0	93	1B_E_2
C			14	0	6	8	14	0	0	0	0	100	0	57	1C_E_2
A	T	2	21	0	15	6	21	0	0	0	0	100	0	29	1A_T_2l
B			14	0	10	3	13	0	1	0	1	93	7	21	1B_T_2
C			14	0	11	3	14	0	0	0	0	100	0	21	1C_T_2
A		3	7	2	0	5	7	0	0	0	0	100	0	71	1A_T_3l
B			14	12	0	2	14	0	0	0	0	100	0	14	1B_T_3
C			14	11	0	1	12	0	0	2	2	86	14	7	1C_T_3

D = Destination (E = Exit and T = Through). N = Number of participants driving a particular testing variation. ✓ = Sum of number of participants with correct lane changes. ✗ = Sum of number of participants with incorrect lane changes % ✓ = Percent of participants with correct lane changes. % ✗ = Percent of participants with incorrect lane changes. % U = Percent of participants with unnecessary lane changes. l 1A_T_3 and 1A_T_2 were each to be tested twice; however, due to a researcher error, 1A_T_2 was tested three times and 1A_T_3 was only tested once.

Key Findings

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. Those 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

Overview

Topic 2 studied signing methods when two interstate exits are within close proximity and there is a need to create signs for three destinations (two interchanges/exits and the through lanes). Figure 21 through figure 23 shows the SSs studied; only 1.5- and 1-mi advance signs were used. It was assumed that the far right lane would be an exit only lane with the second to the right lane being an optional exit for the first interstate exit and then becoming an exit only lane for the second exit. As shown in figure 21, due to the complexity, SS 2-A does not indicate the second exit as an exit only in any manner in the advance signs. SS 2-A has multiple signs with exit only panels, SS 2-B has arrow-per-lane signs, and SS 2-C has diagrammatic signs. Figure 12 presents a graphic of the geometrics for the portion of the road the participants drove along. The simulation ended prior to the participants reaching any of the exits.

Figure 21. Illustration. SS 2-A: multiple signs with exit only panels.

 

Figure 22. Illustration. SS 2-B: arrow-per-lane sign.

 

Figure 23. Illustration. SS 2-C: diagrammatic sign.

Observations

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. Questions asked following the driving portion of this topic included the following:

• 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 change lanes?
• Why did you change lanes (if they moved out of lane 3)?

Note that each participant was assigned one of these codes: C, H, U, IL, IR, IS, and G. If the participant had more than one type of lane change (e.g., both an incorrect lane change to the right (IR) and an unnecessary lane change (U)), the code was assigned in the following priority order: IL, IR, IS, U, C, H, and G.

Table 10. Topic 2: number of participants with lane change type by test variation.

SS	D	SL	N	C	H	U	✓	IL	IS	✗	G	% ✓	% ✗	%G	W	Scenario
A	T	3	7	0	4	3	7	0	0	0	0	100	0	0	9.6	2A_T_3
B			7	0	5	2	7	0	0	0	0	100	0	0	10.0	2B_T_3
C			7	0	4	3	7	0	0	0	0	100	0	0	9.6	2C_T_3
A	T	4	7	0	0	6	6	0	0	0	1	86	0	14	9.7	2A_T_4
B			7	7	0	0	7	0	0	0	0	100	0	0	10.0	2B_T_4
C			7	3	0	4	7	0	0	0	0	100	0	0	7.1	2C_T_4
A	1	2	7	4	0	3	7	0	0	0	0	100	0	0	9.7	2A_1st_2
B			7	2	0	5	7	0	0	0	0	100	0	0	9.6	2B_1st_2
C			7	4	0	3	7	0	0	0	0	100	0	0	8.0	2C_1st_2
A	2	2	7	1	0	0	1	0	0	0	6	14	0	86	7.3	2A_2nd_2
B			7	7	0	0	7	0	0	0	0	100	0	0	10.0	2B_2nd_2
C			7	5	0	0	5	0	0	0	2	71	0	29	6.6	2C_2nd_2
A	2	4	7	0	4	0	4	3	0	3	0	57	43	0	9.3	2A_2nd_4
B			7	0	7	0	7	0	0	0	0	100	0	0	8.9	2B_2nd_4
C			7	0	6	0	6	1	0	1	0	86	14	0	8.0	2C_2nd_4
A	2	5	7	4	0	0	4	3	0	3	0	57	43	0	10.0	2A_2nd_5
B			7	7	0	0	7	0	0	0	0	100	0	0	9.7	2B_2nd_5
C			7	5	0	0	5	1	1	2	0	71	29	0	7.0	2C_2nd_5

D = Destination (T = Through, 1 = First exit, and 2 = Second exit). N = Number of participants driving a particular testing variation. ✓ = Sum of number of participants with correct lane changes. ✗ = Sum of number of participants with incorrect lane changes. %✓ = Percent of participants with correct lane changes. %✗ = Percent of participants with incorrect lane changes. %G = Percent of participants with pregore undetermined lane changes. W = Weighted average for responses to following question: "How confident are you that you picked the correct lane on a scale of 1 to 10 with 10 being the most confident?"

The observations for this topic are as follows:

• Some of the participants may not have made necessary lane changes because the simulation did not include the exits.
• When the participants were told the destination was Longford, Augusta, or Newport
  (i.e., they were to stay on the freeway, variations 2X_T_3 or 2X_T_4), they made correct lane changes in all but one case. Several unnecessary lane changes were made by participants who started in the lane in which they should stay (lane 3, 2X_T_3). When the participants started in lane 4, they needed to make at least one lane change to the left. In all cases but one, the participants made 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.
• When participants were told to go to Hutchinson, Pleasanton, or Henderson (i.e., the first destination, variation 2X_1st_2), all of them 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 participants made the extra unnecessary lane change to lane 5 (i.e., right-most lane), they were coded as being correct but 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 2-B.
• When participants were told to go to Clearwater, Steelville, or Sweetwater (i.e., the second destination, variations 2X_2nd _2, 2X_2nd_4, or 2X_2nd_5), all participants were in the correct lane at the end of the simulation for SS 2-B (arrow-per-lane signs) regardless of the participants' starting lane. Participants seeing SS 2-C (diagrammatic signs) had more correct lane positions than those who saw the multiple signs with exit only panels (SS 2-A) but not as well as for the arrow-per-lane signs (SS 2-B). For those starting in lane 2 and seeing SS 2-A, six of the seven participants (86 percent) had not changed into the correct lane by the end of the simulation.
• The average confidence ratings for SSs A, B, and C were 9.3, 9.7, and 7.7, respectively. Drivers were most confident with their lane choice for the signs that provided an arrow per lane (SS 2-B). Drivers were least confident with the diagrammatic sign (SS 2-C).

Key Findings

For SS 2-B, which had an arrow-per-lane design, all participants (42) made correct lane change decisions. SS 2-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 2-C, only 3 made incorrect lane change decisions. SS 2-A did
not have as favorable results. For example, 6 of the 42 participants made incorrect lane change decisions. SS 2-A also had more of the participants needing additional information to make a lane change decision.

Topic 3

Overview

Topic 3 evaluated signs for an upcoming Y-split. Researchers looked at how quickly drivers made a lane choice and whether one SS better separated drivers into their proper lane for the upcoming Y-split. Signing options included a split sign to explore whether it helps 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 3-A had shared exit signs, SS 3-B had split exit signs both in advance and at the gore, and SS 3-C had shared exit advance signs with a split exit sign at the gore. At the Y-split for SSs 3-A and 3-C, the city exit on top of the sign branched to the left, and the one on the bottom branched to the right.

Figure 24. Illustration. SS 3-A: shared exit signs.

 

Figure 25. Illustration. SS 3-B: split exit signs.

 

Figure 26. Illustration. SS 3-C: shared exit advance signs with split exit gore sign.

The geometry presented to the drivers was three lanes at the beginning with two lanes exiting to the right. The geometry in the simulator showed the exit lanes traveling straight and the through lane curving to the left, as shown in figure 13.

Observations

Table 11 shows a summary of the number of participants with correct, incorrect, unnecessary, and swerve lane changes by test variation for topic 3. Observations for this topic are as follows:

Table 11. Topic 3: number of participants with lane change type by test variation.

SS	D	SL	N	C	H	✓	IL	IR	IS	✗	% ✓	% ✗	S	IC	?	Scenario
A	L	2	7	0	3	3	0	4	0	4	43	57	2	1	3	3A_Left_2
B			7	0	5	5	1	1	0	2	71	29	0	1	1	3B_Left_2
C			7	0	6	6	0	1	0	1	86	14	0	0	0	3C_Left_2
A	L	3	7	0	0	0	0	0	7	7	0	100	0	0	0	3A_Left_3
B			7	6	0	6	0	0	1	1	86	14	0	0	0	3B_Left_3
C			7	4	0	4	0	0	3	3	57	43	0	0	0	3C_Left_3
A	R	2	7	1	0	1	0	0	6	6	14	86	0	0	0	3A_Right_2
B			7	7	0	7	0	0	0	0	100	0	0	0	0	3B_Right_2
C			7	6	0	6	0	0	1	1	86	14	0	0	0	3C_Right_2
A	R	3	7	0	7	7	0	0	0	0	100	0	0	0	0	3A_Right_3
B			7	0	7	7	0	0	0	0	100	0	0	0	0	3B_Right_3
C			7	0	7	7	0	0	0	0	100	0	0	0	0	3C_Right_3

D = Destination (L = Exit ramp lane was on the left for the assigned destination and R = Exit ramp lane was on the right for the assigned destination). N = Number of participants driving a particular testing variation. ✓ = Sum of number of participants with correct lane changes. ✗ = Sum of number of participants with incorrect lane changes. % ✓ = Percent of participants with correct lane changes. % ✗ = Percent of participants with incorrect lane changes. ? = Number of participants making indecisive lane changes. Note the two swerves are associated with the same participant.

Note that each participant was assigned one of these codes: C, H, IL, IR, or IS. If a participant had more than one type of lane change, the code was assigned in the following priority order: IL, IR, IS, C, and H.

When the destination was the left fork (Winner, Edison, or Mission) and drivers started in lane 2 (variation 3X_Left_2), they should not have moved out of the starting lane. SS 3-C had the fewest participants making an incorrect lane change. SS 3-A with the destinations stacked had the most incorrect lane changes, with all 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 3-A (i.e., participants did not recognize that the stacking of the cities was associated with lane position). Only half of the participants did so with SS 3-C, which had stacked city names for the first two signs and the divided sign on the final SB. For SS 3-C, four of the seven participants correctly changed lanes near the third SB (see figure 28). SS 3-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 3-B, this was the initial SB, while for SS 3-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 3-A and were most likely to pick the correct lane with SS 3-B.

Figure 27. Graph. Topic 3 lane change location 3X_Left_2.

Figure 28. Graph. Topic 3 lane change location 3X_Left_3.

Figure 29. Graph. Topic 3 lane change location 3X_Right_2.

Figure 30. Graph. Topic 3 lane change location 3X_Right_3.

Key Findings

For SS 3-B, the split sign was used for the two advance signs and at the gore. SS 3-C only used the split sign at the gore, with the two advance signs showing the destinations vertically stacked. SS 3-A used the vertical stacked format for both the two advance signs and the gore sign. The lateral location of the destination on the sign was used by participants in making a lane change decision. As can be seen in figure 27 through figure 30, several lane changes were made at the first appearance of the split exit sign (at SB I location for SS 3-B and at SB III location for SS 3-C). While several incorrect lane changes were made for each SS, SS 3-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. The AASHTO Guidelines for the Selection of Supplemental Guide Signs for Traffic Generators Adjacent to Freeways provides a basis for the development of State policies for selecting supplemental guide signs for traffic generators adjacent to freeways.⁽⁴⁴⁾ Gore signs with advance signs at 1 mi were used to explore if 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 4-A had a single sign with multiple destinations, SS 4-B had split signs on a single SB, and SS 4-C had sign spreading on multiple SBs. All of the SSs have the exit number panels positioned on the upper right.

Figure 31. Illustration. SS 4-A: single sign with multiple destinations.

 

Figure 32. Illustration. SS 4-B: sign spreading across multiple signs on a single bridge.

 

Figure 33. Illustration. SS 4-C: sign spreading across multiple SBs.

Observations

Table 12 shows a summary of the number of participants with correct, incorrect, unnecessary, and indecisive lane changes by test variation for topic 4. Questions asked following the driving segment included the following:

• What lane would you have gotten in to go to Kenston/Wright/Aspen—left or right?
• Should you have exited if you wanted to go to the convention center?
• How did you know to exit (if they took the exit)?
• How much longer do you drive until you will exit (if they did not take the exit)?

Note that each participant was assigned one of these codes: C, H, IL, IR, or IS. If the participant had more than one type of lane change, the code was assigned in the following priority order: IL, IR, IS, C, and H. Also, a participant could have both a code of IC along with a code of C, H, IL, IR, or IS.

Table 12. Topic 4: number of participants with lane change type by test variation.

SS	D	SL	N	C	H	✓	IL	IR	IS	✗	% ✓	% ✗	IC	?	Scenario
A	C	1	7	4	0	4	0	3	0	3	57	43	0	0	4A_CNV_1
B			7	6	0	6	0	0	1	1	86	14	0	0	4B_CNV_1
C			7	7	0	7	0	0	0	0	100	0	0	0	4C_CNV_1
A	C	2	7	0	6	6	0	0	1	1	86	14	0	0	4A_CNV_2
B			7	0	5	5	0	0	2	2	71	29	0	0	4B_CNV_2
C			7	0	7	7	0	0	0	0	100	0	0	0	4C_CNV_2
A	2	2	7	0	6	6	1	0	0	1	86	14	0	0	4A_2nd_2
B			7	0	2	2	5	0	0	5	29	71	1	1	4B_2nd_2
C			7	0	4	4	3	0	0	3	57	43	2	2	4C_2nd_2
A	1	2	7	0	6	6	1	0	0	1	86	14	0	0	4A_1st_2
B			7	0	7	7	0	0	0	0	100	0	0	0	4B_1st_2
C			7	0	7	7	0	0	0	0	100	0	0	0	4C_1st_2

D = Destination (C = Exit to convention center, 2 = Go to second exit (Kenston, Wright, or Aspen), and 1 = Go to first exit (Fitch, Martin, or Clark). N = Number of participants driving a particular testing variation. ✓ = Sum of number of participants with correct lane changes. ✗ = Sum of number of participants with incorrect lane changes. % ✓ = Percent of participants with correct lane changes. % ✗ = Percent of participants with incorrect lane changes. ? = Number of participants making indecisive lane changes.

Observations for this topic are as follows:

• When participants were told the destination was the convention center (variation 4X_CNV_1 or 4X_CNV_2), SS 4-B and SS 4-A had similar poorer results, indicating these SSs were not as well understood as the sign spreading approach used with SS 4-C. When starting in lanes 1 or 2, participants viewing SS 4-C were always correct. About half of the participants who started in the far left lane missed the exit to the convention center with SS 4-A. Only one of the participants who started in lane 2 missed the convention center with SS 4-A. SS 4-B also was associated with participants who missed the exit to the convention center.
• When participants were told the destination was Kenston Avenue, Wright Avenue, or Aspen Avenue (i.e., second exit; variation 4X_2nd_2), SS 4-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 is the lane that 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.
• When participants were told the destination was Fitch Way, Martin Way, or Clark Way (i.e., first exit; variation 4X_1st_2), almost all of the participants correctly drove these scenarios. 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.

Key Findings

For most of the variations studied, SS 4-C (sign spreading across two SBs) had the most participants making the correct lane-change decision, although SS 4-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 pieces of information on one SB. The question being explored was the following: "Does sign spreading affect where lane changes occur?" As shown in figure 34 and figure 35, SS 5-A did not have sign spreading, while SS 5-B had sign spreading across many SBs. 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.

Figure 34. Illustration. SS 5-A: no sign spreading.

 

Figure 35. Illustration. SS 5-B: sign spreading.

Observations

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. Note that each participant was assigned one of these codes: C, U, IR, IS, or G. If the participant had more than one type of lane change (e.g., both IR and U), the code was assigned in the following priority order: IR, IS, U, C, and G. Also, a participant could have both a code of S along with a code of IR, IS, U, C, or G.

Table 13. Topic 5: number of participants with lane change type by test variation.

SS	D	SL	N	C	U	✓	IR	IS	✗	G	% ✓	% ✗	% G	S	?	Scenario
A	T	4	14	7	7	14	0	0	0	0	100	0	0	0	0	5A_T_4
B			14	10	0	10	0	4	4	0	71	29	0	0	0	5B_T_4
A	O	1	14	9	0	9	1	2	3	2	64	21	14	4	2	5A_Oak_1
B			14	8	0	8	1	2	3	3	57	21	21	2	1	5B_Oak_1
A	L	3	14	13	0	13	0	0	0	1	93	0	7	4	2	5A_Leon_3
B			14	13	0	13	0	0	0	1	93	0	7	2	1	5B_Leon_3

D = Destination (T = Through, O = Oak exit, and L = Leon exit). N = Number of participants driving a particular testing variation. ✓ = Sum of number of participants with correct lane changes. ✗ = Sum of number of participants with incorrect lane changes. %✓ = Percent of participants with correct lane changes. %✗ = Percent of participants with incorrect lane changes. %G = Percent of participants with pregore undetermined lane changes. ? = Number of participants making indecisive lane changes. The two swerves are associated with the same participant.

Observations for this topic are as follows:

• When participants were told the destination was Davenport (i.e., they were to stay on the freeway; variations 5A_T_4 and 5B_T_4), SS 5-A had more unnecessary lane changes compared to SS 5-B—half of the participants with SS 5-A had unnecessary lane changes, while SS 5-B had no unnecessary lane changes. Because SS 5-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 5-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 5-A (see figure 34 and figure 35). SS 5-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-lane exit only lanes. These findings indicate that the position on the SB of the pull-through sign is important.
• When participants were told the destination was Oak Street (i.e., they would need to make a downstream exit to the right; variations 5A_O_1 and 5B_Oak_1), 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.
• When participants were told the destination was Leon (i.e., they would need to make a downstream exit to the left; variations 5A_Leon_1 and 5B_Leon_1), almost all of the participants correctly drove the simulation with both SSs.

Key Findings

The lateral position of a pull-through sign on the SB is important. SS 5-A had more unnecessary lane changes compared to SS 5-B—half of the participants with SS 5-A had unnecessary lane changes, while SS 5-B had no unnecessary lane changes. Because SS 5-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 an unnecessary (but not incorrect) lane change. SS 5-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 as well as if there was confusion on whether it was an exit only or optional exit. As shown in figure 36 and figure 37, SS 6-A had a yellow plaque at the top left, and SS 6-B had a yellow panel at the bottom of the sign.

Figure 36. Illustration. SS 6-A: yellow plaque at top left.

 

Figure 37. Illustration. SS 6-B: yellow panel at bottom of sign.

Observations

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. Note that each participant was assigned one of these codes: C, H, U, or G. If the participant had more than one type of lane change, the code was assigned in the following priority order: U, H, C, and G.

Table 14. Topic 6: number of participants with lane-change type by test variation.

SS	D	SL	N	C	H	U	✓	✗	G	% ✓	% ✗	%G	Scenario
A	T	1	14	0	9	5	14	0	0	100	0	0	6A_T_1
B			14	0	6	8	14	0	0	100	0	0	6B_T_1
A	E	1	14	0	14	0	14	0	0	100	0	0	6A_E_1
B			12	0	12	0	12	0	0	100	0	0	6B_E_1l
A	E	3	14	13	0	0	13	0	1	93	0	7	6A_E_3
B			13	12	0	0	12	0	1	92	0	8	6B_E_32

D = Destination (T = Through and E = Exit). N = Number of participants driving a particular testing variation. ✓ = Sum of number of participants with correct lane changes. ✗ = Sum of number of participants with incorrect lane changes. % ✓ = Percent of participants with correct lane changes. % ✗ = Percent of participants with incorrect lane changes. %G = Percent of participants with pregore undetermined lane changes. 1 The raw simulator data files for two participants were lost due to saving errors, resulting in only 12 participants for 6B_E_1. 2 The researcher opened an incorrect simulator file for one participant, resulting in only 13 participants for 6B_E_3.

Observations for this topic are as follows:

• When starting in lane 1 and being told to go through(variation 6X_T_1), all drivers were in position to correctly stay on the freeway; however, some drivers made 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 6-B. All drivers with SS 6-B correctly identified the ramp as being on the left, whereas only 85 percent of drivers (2 of 14) with SS 6-A did so.
• When starting in lane 1 and being told to exit (variation 6X_E_1), all drivers were in position to exit correctly. Once they reached lane 1, all of the participants correctly stayed in that lane. All participants identified the left exit correctly in the follow-up question.
• When starting in lane 3 and being told to exit (variation 6X_E_3), 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 drivers identified the left exit correctly in the follow-up question.
• Participants' unprompted comments implied that some of them 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 Findings

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 they 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 6-B with the yellow panel at the bottom of sign moved out of the left-most lane (8 of 14) compared to the participants seeing SS 6-A with the yellow plaque at the top left (5 of 14). For this study, the difference between these two SSs was minimal.