Using advanced adaptive cruise control systems to reduce congestion at sags: An evaluation based on microscopic traffic simulation

•3 different ACC systems are developed to reduce congestion at sag vertical curves at freeways.•A way of adapting parameters of ACC is presented.•A traffic state adaptive cruise control adapts parameters based on its own sensing.•Connected ACC adapts parameters based on information from other, surrounding vehicles.•The improved ACC systems efficiently mitigate congestion.