Yellow Bars, a series of yellow lines across the carriageway with the spacing between them reducing as a roundabout is approached, have been in use for many years at at-grade roundabouts on dual-carriageway high-speed roads. A study in 1981 showed a 52% reduction in accidents on approaches treated with the pattern. On high-speed roads, drivers become adapted to the speed at which they are travelling and find it difficult to slow down sufficiently, to a safe speed to negotiate a hazard such as a roundabout. The reverse exponential pattern of Yellow Bars assists them to adopt a safer entry speed. It was anticipated that Yellow Bars would also help drivers leaving motorways at grade-separated junctions, although it was expected that any effect would be less than the at-grade one, as drivers would have made a conscious decision to leave the motorway and would, therefore, be less likely to be surprised by a roundabout ahead. Most motorway slip-roads are too short to accommodate the pattern from Departmental Standard TD 6/79. A reduced pattern of 45 bars was therefore adopted for this evaluation. A trial of Yellow Bar markings at 48 slip-road sites was commissioned by the Transport Research Laboratory on behalf of the Department of Transport Road Safety Division to investigate their effect on accidents. The trial was carried out by The MVA Consultancy. This report describes the conduct of the trial, data collection and analysis. Accident data were also examined using multiple regression techniques for which additional geometric and flow data were collected.

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