Strategies and spacing requirements for lane changing and merging in automated highway systems

In automated highway systems (AHS) vehicles are expected to operate using their own sensing and control systems by interacting with other vehicles and the infrastructure in a way that guarantees safety, stability, and high capacity. We examine various alternative scenaria for merging and lane changing and we present an algorithm for calculating the minimum safety spacing for lane changing (MSSLC); that is, we calculate the intervehicle spacing that the vehicles should maintain during a merging or lane changing maneuver so that in the case where one of the vehicles executes an emergency braking manuever, the rest of the vehicles have enough time and space to stop without any collision taking place. The calculation of the MSSLCs for merging or lane changing maneuvers is more complicated than the calculation of the minimum safety spacing for a longitudinal vehicle following since, in the former case we have to take into account the particular lane-changing policy of the merging vehicle as well as the effect of combined lateral/longitudinal motion during the lane changing maneuver. The braking profiles of the vehicles involved in an emergency scenario during a lane changing maneuver depends on the particular AHS operational concept, i.e., on the degree of communication between the vehicles and between the vehicles and the infrastructure. We consider six different AHS operational concepts; for each concept we consider possible emergency braking profiles and we investigate the effect of the particular operational concept on the MSSLC.