Variable speed limit system in a freeway connected vehicle environment yielded travel time savings of 30 to 80 hours compared to traditional vehicles.
Simulation of a connected vehicle variable speed limit on a two-lane freeway segment.



Connected Variable Speed Limits Control and Car-Following Control with Vehicle-Infrastructure Communication to Resolve Stop-and-Go Waves

Summary Information

This paper presents a proof-of-concept for a connected link-level variable speed limits (VSL) control system with intelligent vehicles equipped with Car-Following Control (CFC) systems. The main objective is to examine the feasibility of the connected control paradigm and to identify potential improvements in control effectiveness.


A VSL control algorithm dedicated to resolve moving jams is employed as the link-level controller, while a CFC algorithm that controls vehicle acceleration based on model predictive control approach is developed and employed by the vehicle-level controller. The two-level controllers are connected via Dedicated Short-Range Communications (DSRC). The connected control system is tested near a freeway bottleneck where CFC vehicles are randomly distributed in the network. Simulation experiments with different penetration rates of CFC vehicles in the network are conducted to test the change in flow characteristics and in control effectiveness. This study compares scenarios with only human drivers and scenarios including intelligent/connected vehicles.


Simulation results show that CFC systems improve traffic efficiency and substantially change flow characteristics. Despite the significant changes in flow characteristics, the connected control concept works without fundamentally changing the VSL algorithm and resolves stop-and-go waves successfully in all the test cases with CFC vehicles in traffic.

Control effectiveness of the connected VSL and CFC control system are improved by 80 vehicle hours of travel time spent (TTS) for VSL and 30 vehicle hours of TTS and CFC, compared to scenarios with all-human drivers. This is thought to be a result of the combination of the presence of CFC vehicles and better compliance of these vehicles to VSL control commands.