Empirical evidences of dynamic speed limit impact on a metropolitan freeway

Some of the most frequently claimed dynamic speed limits (DSL) benefits (e.g. increase of throughput or speed homogenization) still remain a controversial topic among the scientific community, practitioners and society in general. The objective of the paper is to present an empirical assessment of this policy, aiming to provide an insightful response to the main issues related with the aggregated traffic flow behavior. Thanks to the DSL equipments installed over a metropolitan freeway accessing to Barcelona since February 2009, a comparison between non-DSL scenarios (dated on October 2008) and DSL-affected can be performed. For this purpose, a new methodology has been proposed. The whole process excels in being simple, traffic flow theory consistent, achievable with common available traffic data and easily integrable in a programming language. In doing so, a reliable characterization of the traffic flow behavior under DSL strategies has been obtained. Revealing results concerning to the driver’s behavior when facing different speed limits were obtained. The fundamental diagram calibration shows no capacity increments under DSL together with a significant critical occupancy value shift, when are compared with the non-DSL case. It is also reported certain vehicle speed and lane use (i.e. occupancy) homogenization over the DSL controlled sections