Long-term analysis of the impact of longitudinal barriers on motorway safety.

The objective of this study was to assess the influence of longitudinal barriers located on the median strips and hard shoulders of toll motorways on crash severity in vehicles running off the roadway. The study was based on crashes involving injury and property damage only, recorded from 1996 to 2010 on a French toll motorway network of about 2000 km. In run-off from the roadway onto the hard shoulder, injury risk was halved by a longitudinal barrier. A specific one-sided W-beam guardrail ("GS4") appeared to be the best solution for cars, and even for LUVs and trucks. This does not affect the advisability of specific guardrails for bridges or of concrete barriers, when narrow working widths are required. In run-off onto median strips, a specific guardrail ("GS2") appeared to be the most efficient, followed by the three other metal guardrails currently installed. Concrete barriers, however, are much more effective in preventing complete crossing of the median, which is uncommon and mainly involves trucks, but often with very serious consequences. Longitudinal barriers make an important contribution to highway-user safety, providing a "forgiving" infrastructure in the event of a vehicle going off the road, provided that there are very few motorized two-wheel vehicles using the roadway.