Simulation models show that an optimal control speed harmonization strategy can reduce per-vehicle travel time by 28 to 32 percent.

Identifying optimal acceleration/deceleration for speed harmonization.

January 8, 2017

Summary Information

Intersections, merging roadways, speed reduction zones, and driver response to various disturbances are the primary sources of bottlenecks that contribute to traffic congestion. Speed harmonization strategies reduce driver speeds as they approach congestion, slowing the build-up of congestion and enabling quicker dissipation. The objective of this project is to determine the optimal acceleration or deceleration of each vehicle in a way that harmonizes the speed of an increasing number of vehicles at a speed reduction zone on a highway while minimizing rear-end crashes.


Multiple parameter conditions complying with the proposed optimal control algorithm are compared in the VISSIM simulation environment. The optimal control algorithm was found to have a minimum speed of 10 m/s (meters/second), 35 m/s, maximum acceleration 4.5 m/s2, maximum deceleration of -4.5 m/s2, and a minimum gap distance of 20 ft.


The suggested approach was found to reduce travel time by 28 to 32 percent over the base case and 11 to 28 percent over the variable speed limit algorithm.

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Development and Evaluation of Speed Harmonization using Optimal Control Theory: A Simulation-Based Case Study at a Speed Reduction Zone

Author: Hong, Seongah et al.

Published By: Transportation Research Board

Source Date: January 8, 2017



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speed harmonization, travel time, bottlenecks, connected and autonomous vehicles, optimal control, traffic flow

Benefit ID: 2018-01264