Section: New Results

A Time Gap-Based Spacing Policy for Full-Range Car-Following

Participants : Carlos Flores, Fawzi Nashashibi.

Car-Following techniques are a promising solution to reduce traffic jams, while increasing driver comfort and safety. The first version of such systems, Adaptive Cruise Control (ACC), proposes the employment of throttle/brake automation with ranging sensors to regulate the spacing gap with respect to the vehicle in front. Afterwards, the addition of Vehicle to Vehicle (V2V) communication links permits tighter string formations allowing Cooperative-ACC (CACC). The reaction time towards speed changes from forward vehicles can be significantly reduced, given that the ego-vehicle reacts before an spacing error is detected in feedback, employing preceding or leader vehicles' information.

To take further advantage of car-following benefits, a spacing policy is introduced in the control structure in function of the application requirements. In the state-of-the-art approaches, several works have proposed different policies to address performance metrics as: safety, traffic flow increase, stability, string stability, among others. A more complete spacing policy is studied to target all of these criteria for the full speed range and adaptable for both ACC and CACC techniques.

Towards achieving these goals, it is proposed to divide the speed range in low/high speeds and employ a variable time gap setting. A time gap transition from the minimum value for which string stability is ensured to the targeted value in high speeds is suggested. The minimal distance required in case of an unexpected braking on the preceding vehicle is also evaluated to determine the distance to keep at standstill. Both the time gaps and standstill distance are in function of the employed technique–i.e. ACC or CACC–. Among the research lines to be followed, one can mention:

• Development of a robust controller based on fractional-order calculus to achieve a more performing car-following, fulfilling more requirements.

• Further investigation on the effects of communication delays and latency in the V2V links, as well as study different control structures that react not with the preceding vehicle's behavior but also other string members.

• Consider strings which vehicles may account with different dynamics, which introduces perturbations to the car-following control structure.

More detail can be found in [23].