by MSI » Sat Jun 09, 2012 6:32 pm
The following demonstrates many of the flaws in the Yellow light timing arguments against red light cameras:
2012 TRB Report:
Guidelines for Timing Yellow and Red Intervals at Signalized Intersections
Hugh McGee, Sr, Kevin Moriarty,Timothy J. Gates
Available from TRB for $20. Click View PDF and follow instructions to register and order.
ABSTRACT
- The lack of a national standard, recommended practice, or set of guidelines for determining the duration of the yellow change and red clearance intervals for traffic signal timing has left each agency to determine their own practices. The objective of NCHRP Project 03-95 was to develop a comprehensive and uniform set of recommended guidelines for determining safe and operationally efficient yellow and red intervals at signalized intersections. To accomplish this objective, the study established a “state of knowledge” and “state of practice” through a review of existing guidelines and various literature sources, as well as a survey of transportation agency practitioners. The research also conducted a comprehensive national investigation of driver behavior characteristics through an extensive field data collection and analysis effort. These efforts confirmed the accepted values for perception-reaction time (1.0 s) and deceleration rate (10 ft/s2) as well as established 85th percentile speed estimations for through and left-turning vehicles. Justification was also provided for accounting for start-up delay. From the findings, a succinct recommended guideline for timing of the yellow change and red clearance intervals was formulated based on the kinematic equation and its associated variable values. The recommended guideline encourages a uniform practical application, providing a framework that can be easily adopted into transportation agency practice.
CONCLUSION
- This research confirmed that agencies responsible for change interval timing take a widely varied approach in their practices. The extensive field data collection and analysis efforts confirmed the accepted values for perception-reaction time and deceleration rate as 1.0 seconds and 10 ft/s2, respectively. The data also provided a basis for 85th percentile speed estimations for through and left-turning vehicles. Accounting for start-up delay was also justified. From the findings, a succinct guideline for timing the yellow change and red clearance intervals was formulated based on the kinematic equation and its associated variable values. The recommended guideline encourages a uniform practical application, providing a framework that can be easily adopted into transportation agency policy. Assuming there is agreement with and acceptance of the guidelines by the traffic engineering community, there does not appear to be any justification for additional research into this issue, specifically the formulation of the equation and its associated values. However, further research is suggested to evaluate the safety impacts associated with implementing a red clearance interval, as previous studies have yet to conclusively confirm a safety benefit.
SELECTED FINDINGS
For Yellow Change Interval equation they state the following:
- The value recommended for perception-reaction time (t) is 1.0 seconds and for deceleration rate (a) is 10 ft/s2. The value for the approach speed (V) is recommended as the 85th percentile speed determined under free-flow conditions. If the 85th percentile approach speed for through movements is available, then the yellow interval is calculated directly from Equation 4. Since the 85th percentile speed is typically unavailable, it can be assumed as the approach speed limit plus 7 mph, except for left-turn movements (as explained). Table 1 provides yellow intervals based on typical roadway and driver conditions assuming the posted speed limit plus 7 mph for grades in the range of ±4 percent.
Yellow change grade.jpg
The following demonstrates many of the flaws in the Yellow light timing arguments against red light cameras:
2012 TRB Report: [url=http://amonline.trb.org/1sm7e1/1sm7e1/1]Guidelines for Timing Yellow and Red Intervals at Signalized Intersections[/url]
Hugh McGee, Sr, Kevin Moriarty,Timothy J. Gates
Available from TRB for $20. Click View PDF and follow instructions to register and order.
[b]ABSTRACT[/b]
[list]The lack of a national standard, recommended practice, or set of guidelines for determining the duration of the yellow change and red clearance intervals for traffic signal timing has left each agency to determine their own practices. The objective of NCHRP Project 03-95 was to develop a comprehensive and uniform set of recommended guidelines for determining safe and operationally efficient yellow and red intervals at signalized intersections. To accomplish this objective, the study established a “state of knowledge” and “state of practice” through a review of existing guidelines and various literature sources, as well as a survey of transportation agency practitioners. The research also conducted a comprehensive national investigation of driver behavior characteristics through an extensive field data collection and analysis effort. These efforts confirmed the accepted values for perception-reaction time (1.0 s) and deceleration rate (10 ft/s2) as well as established 85th percentile speed estimations for through and left-turning vehicles. Justification was also provided for accounting for start-up delay. From the findings, a succinct recommended guideline for timing of the yellow change and red clearance intervals was formulated based on the kinematic equation and its associated variable values. The recommended guideline encourages a uniform practical application, providing a framework that can be easily adopted into transportation agency practice.[/list]
[b]CONCLUSION[/b]
[list]This research confirmed that agencies responsible for change interval timing take a widely varied approach in their practices. The extensive field data collection and analysis efforts confirmed the accepted values for perception-reaction time and deceleration rate as 1.0 seconds and 10 ft/s2, respectively. The data also provided a basis for 85th percentile speed estimations for through and left-turning vehicles. Accounting for start-up delay was also justified. From the findings, a succinct guideline for timing the yellow change and red clearance intervals was formulated based on the kinematic equation and its associated variable values. The recommended guideline encourages a uniform practical application, providing a framework that can be easily adopted into transportation agency policy. Assuming there is agreement with and acceptance of the guidelines by the traffic engineering community, there does not appear to be any justification for additional research into this issue, specifically the formulation of the equation and its associated values. However, further research is suggested to evaluate the safety impacts associated with implementing a red clearance interval, as previous studies have yet to conclusively confirm a safety benefit.[/list]
[b]SELECTED FINDINGS[/b]
For Yellow Change Interval equation they state the following:
[list][b]The value recommended for perception-reaction time (t) is 1.0 seconds and for deceleration rate (a) is 10 ft/s2[/b]. The value for the approach speed (V) is recommended as the 85th percentile speed determined under free-flow conditions. If the 85th percentile approach speed for through movements is available, then the yellow interval is calculated directly from Equation 4. Since the 85th percentile speed is typically unavailable, it can be assumed as the approach speed limit plus 7 mph, except for left-turn movements (as explained). Table 1 provides yellow intervals based on typical roadway and driver conditions assuming the posted speed limit plus 7 mph for grades in the range of ±4 percent.[/list]
[attachment=0]Yellow change grade.jpg[/attachment]