Impact of Intelligent Cruise Control on Motorway Capacity

The introduction of driver support systems such as (autonomous) intelligent cruise control (ICC) is foreseen within a few years. However, it is still uncertain how these systems will affect traffic-flow characteristics on motorways. A simulation study has been conducted to assess the impacts on roadway capacity more precisely. Ten different ICC designs are investigated and compared with a reference situation without such support systems. The equipment penetration rates of the systems studied varied and were 10, 20, 50, to 100 percent. A capacity analysis was performed for a common bottleneck situation: an on-ramp to a two-lane motorway. On the basis of the simulation results, some unexpected findings emerged. Support systems that support the driver at all speeds and that do not restrict the deceleration level give rise to capacity gains of about 12 percent. However, the first-generation ICC systems will hardly increase traffic-flow performance. A special stop-and-go ICC design did not improve the traffic-flow quality. It was found that, regardless of the ICC type, a headway setting of 1.2 s did not change roadway capacity near an on-ramp bottleneck significantly.