PATH has been studying the traffic impacts of adaptive cruise control (ACC) and cooperative adaptive cruise control (CACC) systems for many years. From 2014 to 2017 PATH conducted this research under the sponsorship of the FHWA Exploratory Advanced Research Program, with cost sharing from the California Department of Transportation. The reports posted here describe the technical results of this research. One of the important and unique elements of this research was the use of mathematical models of the vehicle following dynamics of ACC and CACC vehicles derived directly from experiments on full-scale vehicles, making these models significantly more realistic than the models that have been used in prior studies. The videos posted on this page show some of the experiments that PATH has conducted on CACC systems.
This video shows four Infiniti M56 vehicles using their production ACC systems on I-580 in Richmond, CA, with the first vehicle programmed to follow a speed change profile with acceleration and braking rates of 0.5 m/s/s and 1.0 m/s/s. The video shows this modest disturbance amplified significantly by the following vehicles because of the string instability of the production ACC system, which only enables each of the following cars to respond to the measured speed changes of its immediate predecessor. The response of the fourth vehicle is delayed by about 5 seconds compared to the first vehicle, and its braking is amplified by a factor of three.
M56 Profile CACC Gap 0 6 Full 2
This video shows the same four Infiniti M56 vehicles using the CACC system that PATH implemented on them, using 5.9 GHz communications to share real-time information about their motions. The first vehicle was programmed to follow the same speed profile as in the ACC video, but in this case the CACC system enables all the vehicles to follow the same speed profile as the leader, without noticeable amplification or delay. This shows the ability of vehicle-to-vehicle communication to provide the preview information needed to enable string stable vehicle following control.
Paving the way to Connected Automation-CACC
This FHWA video describes a preliminary implementation of CACC that PATH did for an FHWA project, using five Cadillac test cars owned by the FHWA Saxton Transportation Operations Laboratory.