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CEVMS and Driver Visual Behavior Study - Peer reviewed report

Richmond

The objectives of the second study were the same as those in the first study, and the design of the Richmond data collection effort was very similar to that employed in Reading. This study was conducted to replicate as closely as possible the design of Reading in a different driving environment. The independent variables included the type of DCZ (CEVMS, standard billboard, or no off-premise advertising), time of day (day or night) and road type (freeway or arterial). As with Reading, the time of day was a between-subjects variable and the other variables were within subjects.

Method

Selection of DCZ Limits

Selection of the DCZ limits procedure was the same as that employed in Reading.

Advertising Type

Three DCZ types (similar to those used in Reading) were used in Richmond:

There were an equal number of CEVMS and standard billboard DCZs on freeways and arterials. Also, there two DCZ that did not contain off-premise advertising with one located on a freeway and the other on an arterial.

Table 7 is an inventory of the target employed in this second study.

Table 7. Inventory of target billboards in Richmond with relevant parameters.

DCZ Advertising Type Copy Dimensions (ft) Side of Road Setback from Road (ft) Other Standard Billboards Approach Length (ft) Roadway Type
5 CONTROL N/A N/A N/A N/A 710 Arterial
3 CONTROL N/A N/A N/A N/A 845 Freeway
9 CEVMS 14'0" x 28'0" L 37 0 696 Arterial
13 CEVMS 14'0" x 28'0" R 37 0 602 Arterial
2 CEVMS 12'5" x 40'0" R 91 0 297 Freeway
8 CEVMS 11'0 x 23'0" L 71 0 321 Freeway
10 Standard 14'0" x 48'0" L 79 1 857 Arterial
12 Standard 10'6" x 45'3" R 79 2 651 Arterial
1 Standard 14'0" x 48'0" L 87 0 997 Freeway
7 Standard 14'0" x 48'0" R 88 0 816 Freeway

* N/A indicates that there were no off-premise advertising in these areas and these values are undefined.
Figure 25 through figure 30 below represent various pairings of DCZ type and road type. Target off-premise billboards are indicated by red rectangles.

Photo of an urban freeway curving to the left with few businesses or other buildings visible because of the height of the freeway. A CEVMS billboard is ahead on the right.
Figure 25. Example of a CEVMS DCZ on a freeway.

Photo of a suburban arterial straight-away with buildi, more on the left side.  A CEVMS billboard is ahead on the right.
Figure 26. Example of CEVMS DCZ an arterial.

Photo of an urban freeway curving to the right with natural landscape on both sides.  A static billboard is ahead on the left.
Figure 27. Example of a standard billboard DCZ on a freeway.

Photo of a suburban arterial straight-away with a few buidlings on both sides. A static billboard is ahead on the right.
Figure 28. Example of a standard billboard DCZ on an arterial.

Photo of a freeway coming out of a curve to the left entering a straight-away with natural landscape on both sides.  There are no billboards visible.
Figure 29. Example of a control DCZ on a freeway.

Photo of a suburban arterial straight-away with buildings on both sides.  There are no billboards visible.
Figure 30. Example of a control DCZ on an arterial.

Photometric Measurement of Signs

The methods and procedures for the photometric measures were the same as for Reading.

Visual Complexity

The methods and procedures for visual complexity measurement were the same as for Reading.

Participants

A total of 41 participants were recruited for the study. Of these, 6 participants did not complete data collection because of an inability to properly calibrate with the eye tracking system, and 11 were excluded because of equipment failures. A total of 24 participants (13 male, M = 28 years; 11 female, M = 25 years) successfully completed the drive. Fourteen people participated during the day and 10 participated at night.

Procedures

Research participants were recruited locally by means of visits to public libraries, student unions, community centers, etc. A large number of the participants were recruited from a nearby university, resulting in a lower mean participant age than in Reading.

Participant Testing

Two people participated each day. One person participated during the day beginning at approximately 12:45 p.m. The second participated at night beginning at around 7:00 p.m. Data collection ran from November 20, 2009, through April 23, 2010. There were several long gaps in the data collection schedule due to holidays and inclement weather.

Pre-Data Collection Activities

This was the same as in Reading.

Practice Drive

Except for location, this was the same as in Reading.

Data Collection

The procedure was much the same as in Reading. On average, each test route required approximately 30 to 35 minutes to complete. As in Reading, the routes included a variety of freeway and arterial driving segments. One route was 15 miles long and contained two target CEVMS, two target standard billboards, and two DCZs with no off-pre

ise advertising. The second route was 20 miles long and had two target CEVMS and two target standard billboards.
The data collection drives in this second study were longer than those in Reading. The eye tracking system had problems dealing with the large files that resulted. To mitigate this technical difficulty, participants were asked to pull over in a safe location during the middle of each data collection drive so that new data files could be initiated.

Upon completion of the data collection, the participant was instructed to return to the designated meeting location for debriefing.

Debriefing

This was the same as in Reading.

Data Reduction

Eye Tracking Measures

The approach and procedures were the same as used in Reading.

Other Measures

The approach and procedures were the same as used in Reading.

Results

Photometric Measurement of Signs

The photometric measurements were performed using the same equipment and procedures that were employed in Reading with a few minor changes. Photometric measurements were taken during the day and at night. Measurements of the standard billboards were taken at an average distance of 284 ft, with maximum and minimum distances of 570 ft and 43 ft, respectively. The average distance of measurements for the CEVMS was 479 ft, with maximum and minimum distances of 972 ft and 220 ft, respectively. Again, the distances employed were significantly affected by the requirement to find a safe location on the road from which to take the measurements.

Luminance

The mean luminance of CEVMS and standard billboards, during daytime and nighttime are shown below in table 8. The results here are similar to those for Reading.

Contrast

The daytime and nighttime Weber contrast ratios for both types of billboards are shown in table 8. During the day, the contrast ratios of both CEVMS and standard billboards were close to zero (the surroundings were about equal in brightness to the signs). At night, the CEVMS and standard billboards had positive contrast ratios. Similar to Reading, the CEVMS showed a higher contrast ratio than the standard billboards at night.

Table 8. Summary of luminance (cd/m2) and contrast (Weber ratio) measurements.

  Luminance (cd/m2) Contrast
Day Mean St. Dev. Mean St. Dev.
CEVMS 2134 798.70 -0.20 0.53
Standard Billboard 3063 2730.92 0.03 0.32
Night        
CEVMS 56.44 16.61 69.70 59.18
Standard Billboard 8.00 5.10 6.56 3.99

Visual Complexity

As with Reading, the feature congestion measure was used to estimate the level of visual complexity/clutter in the DCZs. The analysis procedures were the same as for Reading.

Figure 31 shows the mean feature congestion measures for each of the advertising types (standard errors are included in the figure). Unlike the results for Reading, the selected off-premise advertising DCZs for Richmond differed in terms of mean feature congestion; F(3, 36) = 3.95, p = 0.016. Follow up t-tests with an alpha of 0.05 showed that the CEVMS DCZs on arterials had significantly lower feature congestion than all of the other off-premise advertising conditions. None of the remaining DCZs with off-premise advertising differed from each other. The selection of DCZs for the conditions with off-premise advertising took into account the type of road, the side of the road the target billboard was placed, and the perceived level of visual clutter. Based on the feature congestion measure, these results indicated that the conditions with off-premise advertising were not equated with respect to level of visual clutter.

Graph shows the mean feature congestion as a function of advertising condition and road type.  The highest congestion was on the arterial control condition with a mean of about 3.25, while the highway control condition has a mean congestion about 2.75.  The standard advertising condition had congestion means of just over 2.50 on both arterial control conditions and highway control conditions.  The CEVMS advertising condition also had a congestion means of just over 2.50 on highway control conditions and the least congestion means of just under 2.50 on the arterial control conditions.
Figure 31. Mean feature congestion as a function of advertising condition and road type.

Effects of Billboards on Gazes to the Road Ahead

As was done for the data from Reading, GEE were used to analyze the probability of a participant gazing at the road ahead. A logistic regression model for repeated measures was generated by using a binomial response distribution and Logit link function. The resultant value was the probability of a participant gazing at the road ahead (as previously defined).

Time of day (day or night), road type (freeway or arterial), advertising type (CEVMS, standard billboard, or control), and all corresponding second-order interactions were explanatory variables in the logistic regression model. The interaction of advertising type by road type was statistically significant, X2 (2) = 14.19, p < 0.001. Table 9 shows the corresponding probability of gazing at the road ahead as a function of advertising condition and road type.

Table 9. The probability of gazing at the road ahead as a function of advertising condition and road type.

Advertising Condition Arterial Freeway
Control 0.78 0.92
CEVMS 0.76 0.82
Standard 0.81 0.85

Follow-up analyses for the interaction used Tukey-Kramer adjustments with an alpha level of 0.05. The freeway control had the greatest probability of gazing at the road ahead (M = 0.92). This probability differed significantly from the remaining five probabilities. On arterials, there were no significant differences among the probabilities of gazing at the road ahead among the three advertising conditions. On freeways, there was no significant difference between the probability associated with CEVMS DCZs and the probability associated with standard billboard DCZs.

Additional descriptive statistics were computed for the three advertising types to determine the probability of gazing at the ROIs that were defined in the panoramic scene. As was done with the data from Reading, some of the ROIs were combined for ease of analysis. Table 10 presents the probability of gazing at the different ROIs.

Table 10. Probability of gazing at ROIs for the three advertising conditions on arterials and freeways.

Road Type ROI CEVMS Standard Billboard Control
Arterial CEVMS 0.06 N/A N/A
  Left Side of Vehicle 0.03 0.05 0.04
  Road ahead 0.76 0.81 0.78
  Right Side of Vehicle 0.07 0.06 0.09
  Standard Billboard N/A 0.02 N/A
  Participant Vehicle 0.07 0.06 0.09
Freeway CEVMS 0.05 N/A N/A
  Left Side of Vehicle 0.03 0.01 0.01
  Road ahead 0.82 0.85 0.92
  Right Side of Vehicle 0.04 0.04 0.03
  Standard Billboard N/A 0.04 N/A
  Participant Vehicle 0.06 0.06 0.05

The probability of gazing away from the forward roadway ranged from 0.08 to 0.24. In particular, the probability of gazing toward a CEVMS was slightly greater on arterials (M = 0.06) than on freeways (M = 0.05). In contrast, the probability of gazing toward a standard billboard was greater on freeways (M = 0.04) than on arterials (M = 0.02). In both situations, the probability of gazing at the road ahead was greatest on freeways.

Fixations to CEVMS and Standard Billboards

About 2.5 percent of the fixations were to CEVMS. The mean fixation duration to a CEVMS was 371 ms and the maximum fixation duration was 1,335 ms. Figure 32 shows the distribution of fixation durations to CEVMS during the day and at night. In the daytime, the mean fixation duration to a CEVMS was 440 ms and at night it was 333 ms. Approximately 1.5 percent of the fixations were to standard billboards. The mean fixation duration to standard billboards was 318 ms and the maximum fixation duration was 801 ms. Figure 33 shows the distribution of fixation durations for standard billboards. The mean fixation duration to a standard billboard was 313 ms and 325 ms during the day and night, respectively. For comparison purposes, figure 34 shows the distribution of fixation durations to the road ahead during the day and night. In the daytime, the mean fixation duration to the road ahead was 378 ms and at night it was 358 ms.

The table shows the fixation duration on CEVMS billboards during the day and night.  The day time fixation peaks at <300ms (about 40%) with 400-600ms encompassing about 30% of the fixation, 700-800ms encompassing about 20% of the fixation and 900-1,000ms encompassing about 5% of the fixation.  There was no or very little fixation between 1,100-1,400ms; however, 1,500ms showed about 5% fixation.  The night time fixation peaks at <300ms (about 45%) with 400-500ms encompassing about 45% of the fixation, 600-700ms encompassing about 10% of the fixation.
Figure 32. Fixation duration for CEVMS in the day and at night.

The table shows the fixation duration on standard billboards during the day and night.  The day time fixation peaks at <300ms (about 60%) with 400ms encompassing about 20% of the fixation and 500-700ms encompassing about 15% of the fixation.  There was no or very little fixation for 800ms; however, 1,000ms showed about 5% fixation.  The night time fixation peaks at 400ms (about 45%) with 300ms encompassing about 40% of the fixation.  500ms encompassed about 10% of the fixation and 800ms encompassed about 5%.
Figure 33. Fixation duration for standard billboards in the day and at night.

The table shows the fixation duration on the road ahead during the day and night.  The day time fixation peaks at <300ms (about 50%) with 400ms encompassing about 20% of the fixation, 500-600ms encompassing about 20% of the fixation, 700-900ms encompasing about 10% and 1,000->2,000ms encompassing very little or no fixation.  The night time fixation peaks at <3000ms (about 45%) with 400ms encompassing about 25% of the fixation, 500-600ms encompassing about 20% of the fixation, 700-1,000ms encompassing about 10% and 1,100->2,0000ms encompassing very little or no fixation.
Figure 34. Fixation duration for the road ahead in the day and at night.

As was done with the data for Reading, the record of fixations was examined to determine dwell times to CEVMS and standard billboards. There were a total of 21 separate dwell times to CEVMS with a mean of 2.86 sequential fixations (minimum of 2 fixations and maximum of 6 fixations). The 21 dwell times came from 12 different participants and four different CEVMS. The mean dwell time duration to the CEVMS was 1,039 ms (minimum of 500 ms and maximum of 2,720 ms). There was one dwell time greater than 2,000 ms to CEVMS. To the standard billboards there were 13 separate dwell times with a mean of 2.31 sequential fixations (minimum of 2 fixations and maximum of 3 fixations). The 13 dwell times came from 11 different participants and four different standard billboards. The mean dwell time duration to the standard billboards was 687 ms (minimum of 450 ms and maximum of 1,152 ms). There were no dwell times greater than 2,000 ms to standard billboards.

In some cases several dwell times came from the same participant. To compute a statistic on the difference between dwell times for CEVMS and standard billboards, average dwell times were computed per participant for the CEVMS and standard billboard conditions. These average values were used in a t-test assuming unequal variances. The difference in average dwell time between CEVMS (M = 1,096 ms) and standard billboards (M= 674 ms) was statistically significant, t(14) = 2.23, p =.043.

Figure 35 through figure 37 show heat maps for the dwell-time durations to the CEVMS that were greater than 2,000 ms. The DCZ was on a freeway during the daytime. The CEVMS is located on the left side of the road (indicated by an orange rectangle). There were three fixations to this billboard, and the single fixations were between 651 ms and 1,335 ms. The dwell time for this billboard was 2,270 ms. Figure 35 shows the first fixation toward the CEVMS. There are no vehicles near the participant in his/her respective travel lane or adjacent lanes. In this situation, the billboard is relatively close to the road ahead ROI. Figure 36 shows a heat map later in the DCZ where the driver continues to look at the CEVMS. The heat map does not overlay the CEVMS in the picture since the heat map has integrated over time where the driver was gazing. The CEVMS has moved out of the area because of the vehicle moving down the road. However, visual inspection of the video and eye tracking statistics showed that the driver was fixating on the CEVMS. Figure 37 shows the end of the sequential fixations to the CEVMS. The driver returns to gaze directly in front of the vehicle. Once the CEVMS was out of the forward field of view, the driver quit looking at the billboard.

Screenshot illustrates a panaramic video frame that shows glances to a CEVMS billboard located on the left side of a freeway during the day.  This shot shows the billboard the furthest distance from the car.
Figure 35. Heat map for first fixation to CEVMS with long dwell time.

Screenshot illustrates a panaramic video frame that shows glances to a CEVMS billboard located on the left side of a freeway during the day.  This shot shows the billboard the middle distance  from the car.
Figure 36. Heat map for later fixations to CEVMS with long dwell time.

Screenshot illustrates a panaramic video frame that shows glances to a CEVMS billboard located on the left side of a freeway during the day.  This shot shows the billboard the closest distance  to the car.
Figure 37. Heat map at end of fixations to CEVMS with long dwell time.

Comparison of Gazes to CEVMS and Standard Billboards

As was done for the data from Reading, GEE were used to analyze whether a participant gazed more toward CEVMS than toward standard billboards, given that the participant was looking at off-premise advertising. Recall that a sample probability greater than 0.5 indicated that participants gazed more toward CEVMS than standard billboards when the participants gazed at off-premise advertising. In contrast, if the sample probability was less than 0.5, participants showed a preference to gaze more toward standard billboards than CEVMS when directing visual attention to off-premise advertising.

Time of day (i.e., day or night), road type (i.e., freeway or arterial), and the corresponding interaction were explanatory variables in the logistic regression model. Time of day had a significant effect on participant gazes toward off-premise advertising, X2 (1) = 4.46, p = 0.035. Participants showed a preference to gaze more toward CEVMS than toward standard billboards during both times of day. During the day the preference was only slight (M = 0.52), but at night the preference was more pronounced (M = 0.71). Road type was also a significant predictor of where participants directed their gazes at off-premise advertising, X2 (1) = 3.96, p = 0.047. Participants gazed more toward CEVMS than toward standard billboards while driving on both types of roadways. However, driving on freeways yielded a slight preference for CEVMS over standard billboards (M = 0.55), but driving on arterials resulted in a larger preference in favor of CEVMS (M = 0.68).

Observation of Driver Behavior

No near misses or driver errors occurred.

Level of Service

Table 11 shows the level of service as a function of advertising type, type of road, and time of day. As expected, there was less congestion during the nighttime runs than in the daytime. In general, there was traffic during the data collection runs; however, the eye tracking data were recorded while the vehicles were in motion.

Table 11. Estimated level of service as a function of advertising condition, road type, and time of day.

  Arterial Freeway
  Day Night Day Night
Control B A C B
CEVMS B A B A
Standard C A C C

Discussion OF RICHMOND RESULTS

Overall the probability of looking at the forward roadway was high across all conditions and consistent with the findings from Reading and previous related research.(11,9,12) In this second study the CEVMS and standard billboard conditions did not differ from each other. For the DCZs on arterials there were no significant differences among the control, CEVMS, and standard billboard conditions. On the other hand, while the CEVMS and standard billboard conditions on the freeways did not differ from each other, they were significantly different from their respective control conditions. The control condition on the freeway principally had trees along the sides of the road and the signs that were present were freeway signs located in the road ahead ROI.

Measures such as feature congestion rated the three DCZs on freeways as not being statistically different from each other. These types of measures have been useful in predicting visual search and the effects of visual salience in laboratory tasks.(34) Models of visual salience may predict that, at least during the daytime, trees on the side of the road may be visually salient objects that would attract a driver's attention.(47) However, it appears that in the present study, participants principally kept their eyes on the road ahead.

The mean fixations to CEVMS, standard billboards, and the road ahead were found to be similar in magnitude with no long fixations. Examination of dwell times showed that there was one long dwell time for a CEVMS greater than 2,000 ms and it occurred in the daytime on a sign located on the left side of the road on a freeway DCZ. Furthermore, when averaging among participants the mean dwell time for CEVMS was significantly longer than to standard billboards, but still under 2,000 ms. For the dwell time greater than 2,000 ms, examination of the scene camera video and eye tracking heat maps showed that the driver was initially looking toward the forward roadway and made a first fixation to the sign. Three fixations were made to the sign and then the driver started looking back to the road ahead as the sign moved out of the forward field of view. On the video there were no vehicles near the subject driver's own lane or in adjacent lanes.

Only the central 2 degrees of vision, foveal vision, provide resolution sharp enough for reading or recognizing fine detail.(57) However, useful information for reading can be extracted from parafoveal vision, which encompasses the central 10 degrees of vision.(57) More recent research on scene gist recognition1 has shown that peripheral vision (beyond parafoveal vision) is more useful than central vision for recognizing the gist of a scene.(58) Scene gist recognition is a critically important early stage of scene perception, and influences more complex cognitive processes such as directing attention within a scene and facilitating object recognition, both of which are important in obtaining information while driving.

The results of this study do show one duration of eyes off the forward roadway greater than 2,000 ms, the duration at which Klauer et al. observed near-crash/crash risk at more than twice those of normal, baseline driving.(14,53) When looking at the tails of the fixation distributions, few fixations were greater than 1,000 ms, with the longest fixation being equal to 1,335 ms.(53,54) The one long dwell time on a CEVMS that was observed was a rare event in this study, and review of the video and eye tracking data suggests that the driver was effectively managing acquisition of visual information while driving and fixated on the advertising. However, additional work needs to be done to derive criteria for gazing or fixating away from the forward road view where the road scene is still visible in peripheral vision.
The results showed that drivers are more likely to look at CEVMS than standard billboards during the nighttime across the conditions tested (at night the average probability of gazing at CEVMS was M= 0.71). CEVMS do have greater luminance than standard billboards at night and also have higher contrast. The CEVMS have the capability of being lit up so that they would appear as very bright signs to drivers (for example, up to about10,000 cd/m2 for a white square on the sign.). However, our measurements of these signs showed an average luminance of about 56 cd/m2. These signs would be conspicuous in a nighttime driving environment but significantly less so than other light sources such as vehicle headlights. Drivers were also more likely to look at CEVMS than standard billboards on both arterials and freeways, with a higher probability of gazes on arterials.

In this second study, CEVMS and standard billboards were more nearly equated with respect to setback from the road. Gazes to the road ahead were not significantly different between CEVMS and standard billboard DCZs across conditions and the proportion of gazes to the road ahead were consistent with previous research. One long dwell time for a CEVMS was observed in this study; however, it occurred in the daytime where the luminance and contrast (affecting the perceived brightness) of these signs are similar to those for standard billboards.


1 "Scene gist recognition" refers to the element of human cognition that enables us to determine the meaning of a scene and categorize it by type (e.g., a beach, an office) almost immediately upon seeing it.

Updated: 12/30/2013
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