The Protective Effect of Roadside Barriers for Motorcyclists

Objective: Roadside barriers are often deployed between road users and fixed hazards to protect users from injury. However, the United States and Australian Roadside Design Guides do not consider motorcyclists in the risk-based decision process for the deployment of a barrier, because the severity indices for barriers and fixed hazards were developed for passenger vehicles. The aim of the present article is to quantify the protective effect of barriers with regards to motorcyclist injury and to thereby inform the Roadside Design Guides as to the relative severity of roadside hazards and infrastructure for motorcyclists. Method: A retrospective case series study, using linked police-reported road crash and hospital admission data in New South Wales, Australia, from 2001 to 2009 was performed. Crude and adjusted relative risks of motorcyclist serious injury were determined for various fixed objects compared to barriers, using serious injury rates and multiple variable logistic regression. Calculated relative risks compared with guardrail for motorcyclists were compared with those determined from the United States and Australian Roadside Design Guides for passenger vehicle occupants. Results: The study identified 1364 motorcyclists injured as a result of single-vehicle collisions with roadside barriers, trees, utility poles, and other fixed roadside infrastructure. Trees, posts, and utility poles were shown to provide significantly higher risks of serious injury to motorcyclists compared to barriers. This was also found to be true for serious injuries to particular body regions, such as the head, spine, and torso. The results for motorcyclists were in reasonable agreement with those derived from severity indices in the United States and Australian Roadside Design Guides for passenger vehicle occupants. Conclusions: Roadside barriers provide a significant reduction in the risk of serious injury to motorcyclists compared to various roadside hazards. The provisions in the United States and Australian Roadside Design Guides for passenger vehicle occupants are generally applicable to motorcyclists and support the prior and ongoing use of such guides for designing roadsides that reduce the risk of injury to motorcyclists. However, a more realistic estimation might be derived by increasing the severity indices for barriers by around 25 percent for motorcyclists.