Road throughput can be increased by driving at small inter-vehicle time gaps. The amplification of velocity disturbances in upstream direction, however, poses limitations to the minimum feasible time gap. String-stable behavior is thus considered an essential requirement for the design of automatic distance control systems, which are needed to allow for safe driving at time gaps well below 1 s. Theoretical analysis reveals that this requirement can be met using wireless inter-vehicle communication to provide real-time information of the preceding vehicle, in addition to the information obtained by common Adaptive Cruise Control (ACC) sensors. In order to validate these theoretical results and to demonstrate the technical feasibility, the resulting control system, known as Cooperative ACC (CACC), is implemented on a test fleet consisting of six passenger vehicles. Experiments clearly show that the practical results match the theoretical analysis, thereby indicating the possibilities for short-distance vehicle following.

Cooperative adaptive cruise control (CACC) allows for short-distance automatic vehicle following using intervehicle wireless communication in addition to onboard sensors, thereby potentially improving road throughput. In order to fulfill performance, safety, and comfort requirements, a CACC-equipped vehicle platoon should be string stable, attenuating the effect of disturbances along the vehicle string. Therefore, a controller design method is developed that allows for explicit inclusion of the string stability requirement in the controller synthesis specifications. To this end, the notion of string stability is introduced first, and conditions for L ₂ string stability of linear systems are presented that motivate the development of an H _∞ controller synthesis approach for string stability. The potential of this approach is illustrated by its application to the design of controllers for CACC for one- and two-vehicle look-ahead communication topologies. As a result, L ₂ string-stable platooning strategies are obtained in both cases, also revealing that the two-vehicle look-ahead topology is particularly effective at a larger communication delay. Finally, the results are experimentally validated using a platoon of three passenger vehicles, illustrating the practical feasibility of this approach.

Cooperative adaptive cruise control (CACC) is a promising technology that is proven to enable the formation of vehicle platoons with small inter-vehicle distances, while avoiding amplifications of disturbances along the vehicle string. As such, CACC systems can potentially improve road safety, traffic throughput and fuel consumption due to the reduction in aerodynamic drag. Dedicated short range communication (DSRC) is a key ingredient in CACC systems to overcome the limitations of onboard sensors. However, wireless communication also involves inevitable network-induced imperfections, such as a limited communication bandwidth and time-varying transmission delays. Moreover, excessive utilization of communication resources jeopardizes the reliability of the DSRC channel. The latter might restrict the minimum time gap that can be realized safely. As a consequence, to harvest all the benefits of CACC, it is important to limit the communication to only the information that is actually required to establish a (string-)stable platoon over the wireless network and to avoid unnecessary transmissions. For this reason, an event-triggered control scheme and communication strategy is developed that takes into account the aforementioned network-induced imperfections and that aims to reduce the utilization of communication resources, while maintaining the desired closed-loop performance properties. The resulting $\mathcal {L}_{2}$ string-stable control strategy is experimentally validated by means of a platoon of three passenger vehicles.

This paper presents a new method for the design and validation of advanced driver assistance systems (ADASs). With vehicle hardware-in-the-loop (VEHIL) simulations, the development process, and more specifically the validation phase, of intelligent vehicles is carried out safer, cheaper, and is more manageable. In the VEHIL laboratory, a full-scale ADAS-equipped vehicle is set up in a hardware-in-the-loop simulation environment, where a chassis dynamometer is used to emulate the road interaction and robot vehicles to represent other traffic. In this controlled environment, the performance and dependability of an ADAS is tested to great accuracy and reliability. The working principle and the added value of VEHIL are demonstrated with test results of an adaptive cruise control and a forward collision warning system. On the basis of the ‘V’ diagram, the position of VEHIL in the development process of ADASs is illustrated.