Simulation Results Revealed a V2I-based Speed Advisory System Increased the Minimum Time to Collision by an Average of 1.2 Seconds.

Researchers Assessed the Safety Impacts via Traffic Simulations for Connected Vehicles with a Speed Advisory System at Four Signalized Intersections in Atlanta, Georgia.

Date Posted

Safety Benefits of Automated Speed Advisory Systems at Signalized Intersections

Summary Information

Drivers' attempts to reach their desired speed without knowledge of upcoming traffic signals at intersections can cause inefficient human-driving behavior, such as idling or hard braking. This study evaluated the safety impact of connected vehicles equipped with a Speed Advisory System (SAS) that optimizes driving behavior while approaching signalized intersections. Mixed-traffic situations between SAS and Human-Driven Vehicles (HDV) using real world data from Atlanta, Georgia was simulated. HDVs in the model developed in this study followed real vehicle trajectories based on car-following conditions. The study investigated various scenarios including the impact of the different ranks of SAS vehicles in the vehicle group, the lane-changing possibility, and Market Penetration Rates (MPR). 


This study examined the effects of varying levels of SAS MPR (0%, 25%, 50%, 75%, 100%) on rear-end collision risks. Real vehicle trajectories, vehicle lengths, and signal timing were inputted into the model, including trajectory data from the NGSIM project that was collected from four signalized intersections in Atlanta, Georgia in November 2006. The rear-end collision risks were measured by three safety indicators: time to collision (measure time to collision between current and preceding vehicles assuming no change in their speed and direction), deceleration rate to avoid a crash (deceleration required to prevent collision with the preceding vehicle), and crash potential index (probability of current vehicle's DRAC exceeding max deceleration rate).


  • The results suggest that the higher the SAS MPR, the more the conflict-area gradually reallocates from the location near the traffic signal to the location where the V2I communication starts.
  • The minimum time to collision increased by 1.2 seconds and the deceleration rate to avoid crash declined by 0.3 m/s2 on average for 100 percent MPR relative to zero percent. 
  • HDVs following a SAS vehicle could reduce the collision risks by using similar accelerations as the SAS vehicles.
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