Are commercially implemented adaptive cruise control systems string\n stable?

In this article, we assess the string stability of seven 2018 model year\nadaptive cruise control (ACC) equipped vehicles that are widely available in\nthe US market. Seven distinct vehicle models from two different vehicle makes\nare analyzed using data collected from more than 1,200 miles of driving in\ncar-following experiments with ACC engaged by the follower vehicle. The\nresulting dataset is used to identify the parameters of a linear second order\ndelay differential equation model that approximates the behavior of the black\nbox ACC systems. The string stability of the data-fitted model associated with\neach vehicle is assessed, and the main finding is that all seven vehicle models\nhave string unstable ACC systems. For one commonly available vehicle model that\noffers ACC as a standard feature on all trim levels, we validate the string\nstability finding with a multi-vehicle platoon experiment in which all vehicles\nare the same year, make, and model. In this test, an initial disturbance of 6\nmph is amplified to a 25 mph disturbance, at which point the last vehicle in\nthe platoon is observed to disengage the ACC. The data collected in the driving\nexperiments is made available, representing the largest publicly available\ncomparative driving dataset on ACC equipped vehicles.\n