Investigating the Effect of Wireless Communication-Enabled Adaptive Cruise Control on Traffic Smoothing, 10-R9802

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Principal Investigators
Purser K. Sturgeon
Kevin J. Alley

Inclusive Dates:  04/01/08 – 07/01/09

Background - In the past decade, vehicle technology has been moving toward enabling intelligent vehicles, or "smart cars." These vehicles provide technologically advanced active and passive safety, control and communications systems. These systems increase the safety and mobility of vehicles and transportation systems, and R&D is on-going internationally through public and private efforts. SwRI is actively involved in the research and development of the enabling technologies for intelligent and autonomous vehicles through several internal research and commercial programs.

Automotive platforms today implement cruise control through various sensors around the vehicle. Sensors such as radar, sonar, and laser provide a vehicle-centric approach to adaptive cruise control and vehicle platoons/teams. Such systems require the driver to remain actively involved in the system control. In addition, platoons of vehicles are currently not able to cooperatively operate along a roadway. A wireless system or network, enabling vehicle-to-vehicle communications, can pass vehicle-based information to accomplish such an activity. A by-product of "platooning," or cooperative adaptive cruise control, may be traffic smoothing; however, the magnitude of the effect was unknown. Through this program, advanced notification of increased or decreased speed zones has been shown to reduce the traffic caterpillar effect.

Approach - The research conducted on this project analyzed the ability of a cooperative system, utilizing vehicle-to-vehicle communications to improve traffic smoothing. Emphasis was made to investigate the benefits of a sensor-less adaptive cruise control enabled through wireless communications. The key research components were a comparative analysis of the impacts to the string stability, also known as the caterpillar effect, of traffic-jam and convoy operations, and a performance analysis of the system implementations operating in the same environment. The project researched data sets and timing sequences necessary to efficiently exchange information between the vehicles in a platoon, thereby allowing increased performance in vehicle spacing and mobility throughout a highway corridor without the need of extensive and expensive sensors on the vehicles.

Accomplishments - The team completed the development of the on-board vehicle processes for interfacing with each of the vehicle platforms. These processes take different forms because the project used three different vehicle platforms: a traditional human-driven vehicle, a semi-autonomous throttle and brake controlled vehicle, and a fully autonomous vehicle. The onboard processes provide the desired level of control that is required for each vehicle platform. The communications and control code running on the dedicated short range communications (DSRC) radios was consistent in all three vehicles and used a standard message set developed for the SAEJ2735 standard. The project team successfully demonstrated the system using three human-driven vehicles at the ITS America Annual Meeting in Washington, D.C., showing the effectiveness and portability of the system. In addition to this demonstration, SwRI's autonomous vehicle served as the core for a convoy operations demonstration utilizing representative mock-military vehicles for the Robotics Rodeo held at Ft. Hood in September 2009. These demonstrations showed the autonomous vehicle interacting intelligently with human-driven vehicles in a variety of convoy/platooning situations including following a human-driven vehicle(s) in varying formations, dynamically taking over as the lead vehicle in the convoy, and finding and reforming the convoy following events that caused the vehicles to become separated, among other behaviors.

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