The objective of this project was to implement and evaluate a weather responsive traffic signal timing system on Riverdale Road between I-84 and US-89 in Ogden, Utah. The system used road weather information and traffic performance data collected at signalized intersections to enable TMC operators to implement revised signal timing plans and respond to changing traffic demand and travel speeds during severe winter weather events.
Traffic sensors were installed to provide advanced detection upstream of stop bars on Riverdale Road. A weather monitoring station was used to collect information on road temperature, road surface, precipitation, soil temperature, visibility, solar radiation, wind speed, and air temperature.
Controller-based high-resolution detector data were used to automatically generate performance metrics that TMC operators could use to assess the effectiveness of different traffic signal timing strategies and need to change signal timing plans for future events. A software tool (Purdue Coordination Diagram) was used to visualize and optimize signal performance. Intersection approach volume data and link speed data were used by TMC operators to determine when to activate and deactivate signal timing plans, and fine-tune timing parameters.
A Traffic Estimation and Prediction System (TrEPS) tool was used to forecast future traffic conditions and serve as a decision support tool for UDOT operators.
Traffic volume and speed data were collected with and without the system operational to evaluate impacts on travel time and delay. The TrEPS model was used to evaluate impacts.
Interviews were conducted with USDOT and UDOT traffic operators and managers to assess overall effectiveness and perceived benefits in terms of improving traffic signal operations. A total of 13 weather events occurred during the project that were severe enough to warrant implementation of weather responsive signal timing.
Results of operator assessments and modeling indicated that UDOT was able to maintain a high level of progression on Riverdale Rd during inclement weather events. When asked to comment on the overall effectiveness of the system, operators indicated the responsive signal control plans were most effective when minimum recall or no recall plans were used. Operators were less comfortable implementing maximum recall plans and noted the extra stops and additional delays could hinder performance on the main street.
A UDOT traffic signal manager surveyed during the project rated the performance of response plans as average or above average in eight of the 13 events recorded during the project where weather responsive signal timing plans were implemented.
Simulation with Field Data
Modeling results indicated that travel times decreased when weather responsive signal timing plans were implemented instead of normal time-of-day timing plans under similar weather and traffic conditions.
The following bullets summarized overall findings.
- 4.3 percent reduction in cumulative travel time by deploying weather responsive timing plans.
- 11.2 percent reduction in cumulative stop time over using the current time-of-day plans during the snow event.
- UDOT’s weather-responsive signal plans help reduce travel time unreliability for three of the four sections analyzed during the study.
- Modeled results continued to show improvements for all impacted vehicles including cross-street traffic. Cumulative travel times improved by 3 percent and overall stopped times decreased by 14.45 percent.