Two French Hard-Shoulder Running operations: Some comments on effectiveness and safety

This paper describes and analyzes two Hard-Shoulder Running (HSR) operations, which have been implemented in two departments in France. These operations are associated to similar traffic conditions but to different accident contexts and management strategies. Both operations improve traffic capacity locally; however, in the first one, extra traffic is induced and congestion just migrates downstream. As far as safety is concerned, it appears that HSR may increase or decrease the number of accidents, depending on the general accident context, the traffic context, and the active traffic management strategy. This is discussed here. Although the results were not statistically significant in the second operation because of the low accident sample with respect to the low safety impact, safety assessment has increased our knowledge on the managed lanes operations. Issues concerning the statistical assessment method and the minimum number of events (accidents) required for significance tests are also discussed. Surrogate measures may to a certain extent remedy the low sample.