PAPABILES Simulation-based evaluation of the impact of telematics in the Lausanne area: a pilot study

At the present time, variable-message signs (VMS) and variable speed-limit signs are in frequent use for traffic control, especially along urban motorways. The Lausanne by-pass is partially equipped with these and should be fully equipped in the near future. This study is made to evaluate the effects of such systems, either on the efficiency of the road network or the security of its users. The PAPABILES pilot-study deals with the evaluation of the potential effects of such control systems on the performance and safety of the network, using a stateof- the-art simulation tool (MITSIM), developed at the Massachusetts Institute of Technology. In this paper, we present the scenarios that have been tested and comment on the results. Preliminary analysis of the impact of variable speed limit signs made it possible to emphasize the following elements: a) The reduction of the speed limit in the case of high-flow scenarios did not produce a significant increase in the performance of the motorway network, usually limited to 120 km/h. For limitations lower than 100 km/h, it actually seems to decrease. Admittedly, some results tend to show a slight improvement of the performance for speeds around 105 km/h. However, the magnitude of these improvements is too low to justify the installation of such equipment for the sole purpose of increasing the performance of the network. b) About the question of road-users' safety in the presence of high flow, a lower speed limit decreases the probability and the severity of an accident when the traffic breaks down from a normal regime to a congested regime. As mentioned above, this safety improvement does not significantly affect the system's performance in terms of throughput. c) In the case of an incident that notably reduces the capacity of the motorway, simulations carried out up to now show that the application of various speed limitation scenarios does not improve the performance of the network. The capacity of the network is governed by the capacity at the incident location and the actual speed is already below the limitation. Again, the role of speed limitation is more beneficial for safety than throughput. We emphasize that, due to the limited calibration of the model, the results must be interpreted with care. We believe that their interpretation is valid, but that their actual impact must be analyzed in more detail. This will be achieved in subsequent phases of the project.