Content provided in partnership with
Transportation Industry
Benefits of Retiming Traffic Signals, The
Institute of Transportation Engineers. ITE Journal, Apr 2004 by Sunkari, Srinivasa
Temporal (time) constraints are related to a signals inability to consistently provide adequate green time for traffic demand, given competing simultaneous demands from vehicles and pedestrians.
This situation occurs when there is too much traffic for an intersection to physically process, when demand patterns vary to the extent that signal equipment cannot be programmed realistically to accommodate the broad range of hourly/daily/weekly/monthly traffic fluctuations, or when too many conflicting movements require excessive green time (for example, heavy left-turn movements and through movements from multiple approaches at one intersection).
Time constraints also can be imposed by pedestrian signal demands that, with relatively long clearance intervals, may be more demanding of intersection green time than vehicular approaches to an intersection. In addition, the increasing use of emergency vehicle and transit priority and the high-level demand of railroad preemption may mean that green time must be diverted for priority and safety reasons, regardless of capacity conditions at an intersection. Vehicles leaving factories, schools, or other large traffic generators at the same time also can impact traffic severely at a nearby intersection.
HOW OFTEN SHOULD SIGNAL RETIMING BE CONDUCTED?
Signal timing is effective only as long as the traffic patterns that were used to generate the signal timing are reasonably constant. Traffic patterns change over time; developments in surrounding areas also can cause a significant change in traffic patterns.
Existing signal timing cannot operate efficiently with newer traffic patterns. Signal timing should be fine-tuned to operate better. For traffic signals to operate efficiently, the complete retiming of a traffic signal or system often is necessary.
Traffic engineers should review traffic signal and system performance continuously. Ideally, signal timing should be reviewed every year to evaluate effectiveness and efficiency. If necessary, a thorough signal retiming should be conducted. At a minimum, an operating agency should budget to retime traffic signals at least eveiy three years, especially in developing areas and/or areas with sustained growth.
WHAT IS THE COST OF RETIMING TRAFFIC SIGNALS?
Signal retiming often is postponed or ignored due to an agency's financial or staffing constraints. Given the need for field data collection, data analysis, signal timing optimization, testing and implementation, the overall signal timing process can be expensive and time consuming. However, as discussed earlier, retiming traffic signals is necessary to maintain efficient traffic operations.
Estimates of the time required vary according to available expertise and equipment. On average, it is estimated that generating four timing plans (for a.m. peak, noon peak, p.m. peak and off-peak conditions) takes 25 to 30 hours per intersection.
The cost of signal retiming is roughly $2,500 per intersection, including the four typical timing plans. However, a recent signal retiming study in the Washington, DC, USA, area was completed at an average cost of $3,500 per intersection.
Find Research Guides for:
Find Featured Titles for: Technology
Most Popular Articles in Reference
- The importance of understanding organizational culture
- Credit card attitudes and behaviors of college students
- What factors attract foreign direct investment?
- Libraries Need Relationship Marketing - mutual interest marketing concept, ...
- How to set performance goals: employee reviews are more than annual critiques
- More »