Signal retiming projects are fundamental for efficient transportation systems, with the ultimate goal being to minimize the time that vehicles are stopped and delayed at intersections. The U.S. Department of Transportation advises that traffic signal timing should be re-evaluated every 3-5 years, or in any instance where significant changes have occurred. There are numerous benefits to signal retiming, including: reducing congestion and driver frustration, increasing safety, and the reduction of negative environmental impacts, such as air pollution. There are also challenges to implementing signal retiming projects, such as budget constraints and limited resources for staffing and field data collection. Despite these challenges, signal retiming is an efficient way to optimize your transportation systems. Here are 5 key steps to consider for your traffic signal retiming project:

1. Project Scoping

The main goal of the project scoping stage is to identify your problems and determine your objectives. Objectives may include reducing stops, delays, and travel time for a particular corridor. Once you have identified your problems and objectives, you can identify which signals should be included in the section your project will focus on. The smaller the section, the easier it is to optimize and manage data. Once you have your section, select your performance measures and choose your timing plans.  

Myth Buster: While sections need to be on the same timing plan, the included intersections do NOT need to use the same cycle length!  

2. Data Collection

Data collection is integral to the signal retiming project, and there’s a range of data you need to capture for your project, which can often be costly and labor intensive.  

  1. Traffic Volumes – Collecting weekly traffic volumes at relevant locations is important for your data collection efforts, and can help you identify the number of timing plans, when to transition timing plans, volume adjustment factors for the development of turning movement counts, and directional distribution of traffic. The fastest and most cost-effective method for collecting traffic volumes data is the use of system detectors. In the absence of permanent detectors, temporary manual or video counts can be used. 
  1. Turning Movement Counts – These counts are usually collected at each of the intersections undergoing retiming, and should occur consistently during peak periods, which can be informed by the traffic volumes data. The count should include all traffic at the intersection, and can be categorized by directional approach, movement, and traffic type (e.g., pedestrians or car traffic). To collect turning movement count data, either manual counts or video recording can be utilized. Manual counts require positioning staff at intersections during peak periods to manually count movements, whereas video footage can be reviewed and logged after collection from the workplace.  
  1. Vehicular Speed – Vehicular speed measures intersection approach speeds. These speeds can be accurately and efficiently captured for large vehicle quantities using traffic re-dentification, such as Bluetooth and WiFi sensors, or speed detection sensors, such as radar or crowd-sourcing data.  
  1. Travel Time Runs – Travel time runs examine average travel times, intersection delays, intersection stops, and speeds. Travel time can be collected by driving the corridor and recording data, but this is inefficient and difficult to execute during evenings, weekend peaks, or special events. Travel time data can be collected more efficiently, cost-effectively, and on a larger scale using crowdsourcing data.  

The City of Ottawa, in Ontario, Canada, for example, has at least 7 timing plans per intersection in order to streamline traffic flow for various days, times, and weather conditions. Data collection is necessary to optimize these timing plans and effectively reduce traffic congestion.  

3. Model Development

The next step is to create an analytical simulation model. For this, you will first choose a software model and review relevant standards and conditions. Next, you will build your traffic network and enter your data. Simulation models, such as VISSIM and Synchro, allow you to optimize the signal plans and view dynamic data visualizations, including the movement of vehicles, pedestrians, and bicyclists at selected intersections. Finally, you will draft and finalize your timing plan and time-of-day (TOD) schedule.  

4. Field Implementation and Fine Tuning  

This is the step where you implement your study and observe it in practice. The U.S. Department of Transportation recommends that observation should last for a minimum of three days, or two days for weekend schedules. It is at this point that you may wish to carry out a before-and-after study in order to determine project effectiveness. Using software, such as the use of SMATS’ iNode by the City of Ottawa, is a cost-effective way to carry out these studies and quantifiably measure results.  

5. Evaluation of Timing  

Similar to step 4, this is where the final evaluation of the signal retiming project occurs. This may involve verifying project consistency with relevant policies, listening to public opinion, and conducting travel time studies. Travel time studies are often included in reports to elected officials, and can be an easy, low-cost way to quantifiably measure and report improvements. This step is also where you will prepare any final reports, utilizing your collected data and before-and-after study.  

Signal retiming has numerous benefits, and can help your City reduce congestion, increase safety, and reduce negative environmental impacts. Signal retiming is an integral way to support your infrastructure projects while getting a high ROI!  

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Want to learn more? Here is a signal retiming project by the Florida Department of Transportation aimed at reducing off-ramp queue wait times in real time.