The US has about 300,000 traffic signals and Canada has about 50,000. Many of the signals could improve their operations simply by adjusting the timing and/or updating equipment. Signal optimization is one of the most cost effective measures that can significantly reduce congestion and help with traffic flow on arterial roads.
Unfortunately many public agencies only update signal timing if it’s routine or emergency maintenance due to lack of resources such as funding or the manpower for maintaining a comprehensive process that takes time of day/week/season into consideration.
However, agencies that have completed signal retiming projects experienced many improvements in overall traffic conditions. According to the Institute for Traffic Engineers (ITE), past signal timing projects have demonstrated benefit-to-cost ratios of 40:1 or more. The ITE suggests that traffic engineers should annually review the signal timing process to assess its effectiveness and should retime signals every three years.
According to the graph below, nearly 60% of respondents indicated 5+ years for signal retiming, significantly below the standards outlined by the ITE.
Signal Retiming in the Washington, DC Area
In 2002, the Transportation Planning Board in the Washington, DC metropolitan area implemented a traffic signal optimization program that would reduce travel delays and help reduce air pollution. The focus for this signal optimization project was two separate arterial corridors that crossed jurisdictional boundaries and were independently controlled by the state DOTs, cities, and counties.
After conducting traffic studies, observations, and vehicle test runs, The Maryland State Highway Administration estimated the following annual savings: 950,000 vehicle-hours of delays, 320,000 gallons of fuel, 5.5% in hydrocarbon emissions, and 0.5% in nitrogen dioxide (NOx) emissions. After the signal optimization, the average vehicle speed was up 62% to 13.5 mph from 8.3 mph. They also made the assumption that with vehicle delay hours valued at $10 per hour, the benefit achieved was an estimated $19 million over two years, while the project’s cost was $100,000.
Signal Retiming Close to Home
In Waterloo Region, 89 signals were retimed which included arterials on commuter routes and within the downtown core. The Region reduced 10% in travel time, 27% in delays and 20% in stops. This retiming project was completed in 1996 – about 16 years ago. The population has increased by about 100,000 residents or over 20% within that time, not to mention expansions within the overall transportation network. If signals aren’t retimed regularly, the benefits initially achieved erode over time due to growth.
Signal retiming is imperative for public agencies to complete regularly. Budgets should be reallocated to make this a consistent process rather than ad hoc. The ITE provides a guide on traffic signals which breaks down a lot of information and steps for auditing signals.
Traffic Data Collection for Signal Retiming
Data collection is an important stepping stone to understanding the current traffic needs of signalized intersections. Miovision’s traffic data collection equipment, Scout, provides versatility, accuracy and portability which supports signal optimization initiatives.
Using a portable unit benefits projects such as signal optimization where the study location is always changing. Automated data collection, such as the Scout unit, eliminates manual traffic data collection which reduces the amount of time needed to collect data. According to the graph, about 12-14 hours are spent on data collection. Using Miovision’s automated unit, this time can be less than 30 minutes with total setup/take down time and file uploading for processing.
With accuracy of 95%+ in turning movement counts, you can feel confident in the traffic data you are collecting for signal retiming.