The Travel of Errant Vehicles After Leaving the Carriageway

The report focuses on how and where errant vehicles travel after leaving the carriageway on the nearside, the factors that influence that travel and their relative significance. The report includes both international literature and available British data. It covers the distribution of encroachment angles, frictional resistance during run off, the effect of slope on the likelihood of rollover, the severity of injury resulting from hitting different roadside objects and accident data on the combined effect of these factors.

In the UK, a 3.3m hard shoulder is standard on motorways, whilst a 1m strip is used on both single and dual-carriageway trunk roads.  There is no 'clear zone' as such and therefore research has tended to focus on assessing when it is necessary to provide a safety barrier to prevent errant vehicles hitting a roadside object. This required a model to be developed that allows this need to be evaluated for a variety of different roadside conditions. Consequently, an Excel based risk assessment tool the 'Road Restraint Risk Assessment Process' (RRRAP) was developed and is used in tandem with the standard TD 19/06, 'Requirements for Road Restraint Systems' to determine the length and containment level of barrier required to protect a hazard.

You can download a copy of this report in PDF format below: