Video platooning: ACC and CACC compared.mpg





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Uploaded on Jul 14, 2010

The driving behavior of an ACC and CACC system are compared in this video. Normally, the ACC system uses radar to measure the inter-vehicle distance and relative velocity between vehicles. In addition, CACC uses wireless communication to transmit the acceleration from vehicle to vehicle. The robots do not have radar. Wireless communication is used to transmit the position, velocity and acceleration from robot to robot.

The stops and starts of the leading robot simulate driving behavior in a traffic jam. Each robot has a desired time-gap of 2 seconds, which is sufficient to damp out any oscillating driving behavior for ACC in this case. This is called string stability. Traffic shockwaves are prevented and the last robot enjoys fuel economic driving behavior. However, the large distances do not contribute to increasing the traffic throughput.

To increase traffic throughput, the time-gap is decreased to 0.2 second. However, the robots are not able to react fast enough with the ACC system. As a result, the oscillating behavior of the leading robot is amplified from robot to robot, resulting in a traffic shockwave. This is called string instability.

Communication of the acceleration from robot to robot enables the CACC system to react much faster. In this case, a time-gap of only 0.2 second is sufficient to (slightly) damp out the oscillating behavior of the leading vehicle: the string of robots is stable. The prevention of traffic shockwaves combined with small distances clearly shows the benefit of CACC compared to ACC in terms of traffic throughput.


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