The Application of Cooperative Variable Speed Limit Control for Reduction of Crash Potential

Motorways are designed to sustain higher speeds of traffic flows on them. Safety on motorways can be reduced even with the smallest fluctuations in its traffic flows. Those fluctuations can be induced by aggressive traffic lane changing, bad weather or bad road surface conditions, day/night visibility constraints, merging of the vehicles from on-ramps, or sudden and unpredictable breaking of upstream vehicles. All mentioned can be considered as the precursors of potential crash risk. In order to alleviate that risk, it is imperative to apply adequate methods from the domain of intelligent transport systems (ITS) such as Variable Speed Limit Control (VSLC). Primary role of VSLC is to adjust speed limits in order to improve the safety and produce better performance of traffic flows on the motorway. Classic VSLC depends upon driver obedience to the speed limits posted on the VMS in a discrete way, while intelligent speed adaptation (ISA) can induce smooth speed transitions of the vehicle according to the advised or directly imposed speed limits. Special emphasis is set on the cooperative concept which enables the exchange of information between ISA, vehicles, and road side units (RSU) in order to reduce crash risk potential.