INDOT was requested to provide warning signs to be placed at the study intersection to create public awareness of the presence of the video cameras. The success of the program mainly depended on the extent of public awareness and support. Figure 5.3 shows the warning signs used at the intersection. The word ‘monitored’ was used, since the camera system was not used to enforce the red signal compliance. Also, the video equipment and technology used did not allow us to recognize the license plate numbers.
FIGURE 5.3 Photo-enforcement warning signs
These warning signs themselves created significant concern among drivers, which was reported in the local newspapers. Figure 5.4 shows a photo that appeared in the Purdue Exponent. The text below it misinterprets the signs. Despite our best efforts to send a clear message through the signs, the photo publicized in the newspaper indicates that misinterpretation of the signs by some drivers was possible.
The warning signs were deemed to be visible enough to inform drivers of the presence of the camera. The signs were placed a good distance from the intersection so drivers could read and understand the signs and have time to react. Figure 5.5A and Figure 5.5B show the warning signs with the test intersection in the background. Figure 5.6 is a schematic of the intersection with the location of these warning signs.
The intersection was monitored between March 6 and March 28, 2002. The signs were placed at the intersection between March 18 (Monday) and March 25 (Monday). The entire period of analysis is divided into four different periods as was done in the case of police enforcement. The direct observation method was used to record the violations. Video material recorded for six hours from 7 AM to 10 AM and from 3 PM to 6 PM was watched for every other day of the study period. Table 5.10 shows the periods, the days with traffic monitored, and other characteristics of the period. A total of 63 hours were monitored during the entire period.
TABLE 5.10 Periods for Studying the Photo-Enforcement Effectiveness
Period# Dates Included # Hrs Photo
Enforcement Vacation 7 Mar 2002 - 6,7,8 9 No No 8 Mar 2002 - 10,15,16 18 No Yes 9 Mar 2002 - 18,20,22 18 Yes No 10 Mar 2002 - 24,26,28 18 No No Total 63 5.6.2 Discussion of Results
The number of signal cycles in each 15-minute interval was extracted for the entire day as explained previously. The opportunity was then evaluated and the violation rates/frequency were estimated for each period. Only periods 7, 9, and 10 were
FIGURE 5.5A Photos of the warning with the intersection in the background
EB
The signals are circled
NB
The signals are circled
FIGURE 5.5B Photos of the warning with the intersection in the background (continued)
SB
We cannot see the intersection signals here, but the stop can be recognized from the waiting traffic. The first car in the queue is circled.
WB
The signals are circled
FIGURE 5.6 Schematic representation of the intersection showing the location of warning signs Warning Sign Northwestern Avenue Stadium Avenue 360 ft 600 ft 295 ft 250 ft NB SB EB WB WarningSign Warning Sign Warning Sign
considered for the evaluation of photo-enforcement. Approximately 45 hours were observed for the photo-enforcement period and 35 violations were recorded. Period 8 was used in the evaluation of the effect of the presence of students on RLR (Chapter 6). The results are shown in Table 5.8. The violation rate reduced 62% during the week of photo- enforcement (2% significance level). Oxnard, California, and Fairfax, Virginia, (FHWA, 2000G) reported a reduction of 40% in the violation rate. While only a 34% reduction was observed in New York, Howard County observed a 58% reduction. These cities also found that the collisions at intersections declined considerably. New York had a 65% reduction while Oxnard and Fairfax had 22% reductions. The reduction in crashes at different intersections in Howard County varied between 18% and 44% (see Section 5.1).
Drivers responded to the warning signs without any delay but they also had a tendency to return to the pre-enforcement behavior faster than in the case of the police enforcement. The RLR rates of periods 7 and 10 indicate that the residual effect a week after the photo-enforcement was 35% of the original value (19% significance level). This difference in driver response can be explained by the conspicuity of the warning signs. The effect of police enforcement appears to have lasted for a longer period of time. The violation rate in period 7 was not only lower than that in period 1 but also nearly equal to that in period 5. The RLR frequency for period 9 was 50% which was considerably higher than the RLR rates. The discrepancy between the trends in the RLR frequencies and rates were larger than for the police enforcement.
TABLE 5.11 Evaluation of Photo-enforcement
Period# #RLR # Hrs Frequency RLR Opportunity RLR Rate
7 13 9 1.4 263.95 0.049
9 10 18 0.6 522.14 0.019
10 12 18 0.7 375.56 0.032
TABLE 5.12 Significance Levels for Reduction in Violation Rates During Photo Enforcement
First
Period RLR Rate
Second
Period RLR Rate Total RLR
Prob. Of Success Significance Level 7 0.049 9 0.019 23 0.336 0.020 7 0.049 10 0.032 25 0.413 0.187 5.6 Summary
Both the police and photo-enforcement resulted in a significant reduction in the number of violations. Police enforcement resulted in a reduction of only 9% during the week of enforcement, while photo-enforcement showed a reduction of 62%. The reduction in RLR in the period immediately following the police enforcement was 75%, while it was 35% for photo-enforcement. The violation rate in the after-period of photo- enforcement appeared to return to normal at a faster rate than during the police enforcement period, which could be due to drivers’ uncertainty about the police presence.