Engineering Evaluation of Traffic Signal Timing (Short Ambers)

Traffic Engineering report prepared July 20th, 2017


This is an engineer's 35 page report outlining an analysis, discussion, evaluation and sound engineering practice for establishing amber light timing.

This report was created as a result of a Winnipeg citizen, a Mr Aisaican-Chase having received a photo enforcement ticket at the intersection of Bishop Grandin Blvd and River Road, in Winnipeg, Manitoba Canada.  The ticket alleged that Mr. Aisaican-Chase went through the light 0.2 seconds late.  

REPORT INTRODUCTION:  It was reported that, on October 16, 2015, Mr. Jim Aisaican-Chase was travelling westbound on Bishop Grandin Boulevard near its intersection with River Road. As he approached the intersection the traffic light he was facing changed from Green to Yellow.

Mr. Aisaican-Chase continued through the intersection at a constant speed of 80 km/h, and was issued a violation for entering the intersection facing a Red traffic signal.

It is understood that, within the City of Winnipeg, all Yellow traffic signals had a duration of 4.0 seconds. This was the case at all signalized intersections.

The posted speed limit range for intersections in Winnipeg was reportedly between 30 km/h and 80 km/h. The intersection at Bishop Grandin Boulevard & River Road had a posted speed limit of 80 km/h and was equipped with a Red light camera.

On June 19, 2017, Roar Engineering was retained to conduct an independent assessment of Mr. Aisaican-Chase’s traffic violation. Specifically, Roar Engineering was asked to comment on the appropriateness of a 4.0 second Yellow traffic signal duration, and whether or not Mr. Aisaican-Chase’s decision to proceed through the traffic signal was reasonable under the circumstances. 


 See the full report -

ENGINEERING EVALUATION OF TRAFFIC SIGNAL TIMING


 REPORT CONCLUSIONS:

1. The ITE formula for Yellow traffic signal duration is based on the kinematic equations.

2. The speed of traffic on any given roadway is a distribution, not a discreet value.

3. Traffic on any particular roadway travels faster than the Posted Speed Limit. As such, the Design Speed (Posted Speed Limit + 10 km/h) is a more appropriate speed to use when calculating Yellow traffic signal durations.

4. The perception and response time of drivers responding to changing traffic signals is a distribution, not a discreet value.

5. The average driver requires at least 1.0 seconds to perceive and respond to a traffic signal which has changed from Green to Yellow. As such, at least 1.0 seconds should be used when calculating Yellow traffic signal durations.

6. Deceleration rates of vehicles as they approach a planned stop are a distribution, not a discreet value.

7. The average driver decelerates at a rate of 10 ft/s2 or less when approaching a planned stop, such as a Yellow traffic signal.

8. The approach grade for each intersection must be evaluated on an individual basis.

9. The recommended Yellow traffic signal duration for a roadway with a Posted Speed Limit of 80 km/h is 5.2 seconds.

10. A Dilemma Zone exists when the distance required to stop (including the perception and response) exceeds the distance travelled during the Yellow signal.

11. For the recommended Yellow traffic signal durations, no Dilemma Zone exists.

12. If the Yellow traffic signal duration was increased to 5.2 seconds from 4.0 seconds, 88 - 93% of the Red light violations would not have been issued at Bishop Grandin Boulevard & River Road.

13. Dilemma Zones exist for Yellow traffic signal durations of 4.0 seconds on roadways with Posted Speed Limits of 60 km/h or greater. R17R06031 Final Report Page 35 of 35

14. If a constant deceleration rate is required to stop for each different speed zone within the City of Winnipeg, the PRT required to stop decreases as the Posted Speed Limit increases. In the case of an 80 km/h speed zone, the PRT required becomes negative, meaning that the driver must anticipate the changing traffic signal and respond before it changes.

15. If different deceleration rates are required to stop for each different speed zone within the City of Winnipeg, they exceed the recommended 10 ft/s2 , and often exceed what a typical driver could accomplish given the variable weather conditions in Winnipeg.

16. Drivers decelerate at a higher rate when travelling at a higher speed. However, this effect does not justify the high decelerations required, in some cases as high as 13.7 ft/s2 .

17. The Yellow traffic signal duration should be revisited and modified to use the ITE formula in order to prevent severe vehicular collisions, specifically on roadways with Posted Speed Limits above 60 km/h.

18. Mr. Aisaican-Chase found himself within the Dilemma Zone, and could neither continue through the intersection nor decelerate at a reasonable rate without committing a violation.

19. In order to stop by decelerating at a reasonable rate, Mr. Aisaican-Chase would have had to perceive and respond to the changing traffic signal in 0.65 seconds, a duration approximately half that which would be expected of a typical, attentive driver.

20. The decision by Mr. Aisaican-Chase to proceed through the intersection at a constant speed of 80 km/h was reasonable and represented the safest option.

21. The deficient Yellow traffic signal duration on Bishop Grandin Boulevard & River Road was the largest contributor to Mr. Aisaican-Chase’s violation.


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See Also - SHORT AMBER TIMES - THE DILEMMA ZONE


MANUAL FOR UNIFORM TRAFFIC CONTROL & DEVICES (CDN)