The Road Restraint Risk Assessment Process (RRRAP) is the risk-based methodology set out in CD 377 'Requirements for Road Restraint Systems', part of the Design Manual for Roads and Bridges (DMRB). CD 377 replaced the former TD 19/06 standard and reflects the move away from a prescriptive approach to safety barrier provision towards one based on the assessment of risk at individual sites.
RRRAP is used to determine whether a vehicle restraint system (VRS) is justified at a particular location, and, where one is required, to inform its type, length and performance specification. The process weighs the likelihood and severity of a vehicle leaving the carriageway against the risk presented by the roadside hazard itself, recognising that a restraint system is not always the safest or most appropriate solution.
When RRRAP applies
CD 377 and the RRRAP methodology are primarily intended for the strategic road network - motorways and trunk roads managed by National Highways and its counterparts in Scotland, Wales and Northern Ireland. It has not been developed to assess risk on roads with speed limits below 50mph or on lower flow routes, which is why separate guidance exists for the local road network (see below).
What the process involves
- Identification and classification of roadside hazards, such as embankments, structures, water, rigid objects and other features
- Assessment of the likelihood of a vehicle leaving the carriageway and reaching the hazard
- Evaluation of the consequences to different road users if the hazard is struck, against the consequences of a vehicle striking a restraint system instead
- Selection of an appropriate containment level, working width and performance class in line with BS EN 1317
- Consideration of alternatives to a VRS, such as hazard removal, relocation or protection
- Recording the assessment and rationale to provide a clear audit trail for the design decision
Our experience
MERAKI has extensive experience carrying out RRRAP assessments in accordance with CD 377 for both new schemes and existing routes where restraint systems are due for renewal, are life-expired, or where a change in the roadside environment requires the provision to be reviewed. Our engineers are experienced in balancing the technical requirements of CD 377 with practical, cost-effective outcomes for our clients, and in presenting the results of an assessment clearly to support scheme approval.
