The study considered safety alongside all purpose high speed dual-carriageways on behalf of the AA and the Highways Agency. These roads can have either two or three lanes but are generally lower standard than motorways, whether because they have greater values of bendiness and hilliness or because junctions are not necessarily grade-separated. They mostly have a metre strip rather than the full-width 3.3m hard shoulder found on motorways. They have lay-bys at intermittent intervals and occasional service areas. In general, there are no emergency roadside telephones on these roads, although there are occasional public telephones in lay-bys. A metre strip allows light vehicles to get partly off the road, but does not accommodate heavy vehicles; a broken-down vehicle will cause an obstacle as it cannot easily be overtaken at speed or by heavy vehicles without encroaching into the next lane. The case for provision of vehicle refuges (emergency lay-bys) was investigated by undertaking video recordings on the A303 and the A34. Accident risk in a lay-by and of vehicle break-down on the main carriageway are compared with that on motorway hard shoulders and that of driving along the dual-carriageway or motorway.
Abstract