The expected effectivity of the dynamic speed limit algorithm SPECIALIST - A field data evaluation method

Shock waves on freeways can be resolved by dynamic speed limits. In an earlier publication we presented an approach to solve shock waves based on shock wave theory, the so-called SPECIALIST algorithm, and the potential of the algorithm was established by simulation. In this paper a method is presented to evaluate the expected effectivity of the SPECIALIST algorithm based on field data. The effectivity depends on several factors that determine together whether a certain shock wave is solvable or not. The most important factors are (1) the traffic state in and around the shock wave, (2) the value of the displayed speed limits in combination with the compliance of the drivers with the displayed speed limits, and (3) the delay between the traffic state measurements and the actuation of the speed limits. To evaluate the expected effectivity of SPECIALIST an algorithm is developed that identifies the shock waves and their relevant properties in the data and evaluates the solvability per shock wave. The presented methodology is applied to traffic data from the A12 freeway in the Netherlands for 87 morning peaks. The frequency of the occurrence of solvable shock waves is determined as a function of the effective speed limit and the delays in the system.