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Single lane roads with edge strips for bicycles

Since access roads are a category within the Sustainably Safe Programme, they should also be made recognisable as a category. Outside urban areas, this can be done by introducing edge strips on both sides for cyclists and reserving the single traffic lane between them for motor vehicles. But is this the best way, in terms of road safety, to standardise this type of road? Furthermore, can or should carriageways with edge strips start applying as a guideline for access roads?

In elaborating a system of sustainably safe road traffic, the uniformity in road design and traffic engineering measures is an important point requiring attention. Uniformity is a way of procuring the recognisability and predictability of critical traffic situations. The set of revised guidelines for the design of rural roads, motorways excluded (RONA), also assumes the importance of the uniformity of roads.

The uniformity of access roads outside urban areas (60 km/hour) could be increased by introducing a single lane for car traffic in the middle of the carriageway. This lane would be indicated by means of broken lines. The remaining space consists of two edge strips on either side of the road, intended for cyclists. These edge strips would sometimes be made of red asphalt. Various professional and research organisations are recommending the application of this carriageway design.

The SWOV Institute for Road Safety Research has conducted various studies into the effect of 'single lane access roads' on road safety. In its publication entitled R-99-19, SWOV reported on a comparison between access roads with and without such a single lane. The conclusion was that roads with a single lane and edge strips displayed a somewhat lower average driving speed than roads without this layout. Also concluded was the fact that the space between cyclists and passing cars is somewhat smaller on roads with edge strips than on roads without edge strips. SWOV then conducted a study into traffic situations on roads before and after a single lane was introduced (before and after studies). A report on each of these roads is being published, followed by a summary report.

A tentative conclusion from these before and after studies is that the average driving speed is sometimes reduced by a few kilometres per hour on roads with a single lane and edge strips. It also appears that cyclists use "their" lane and usually start cycling farther from the edge of the road than in the previous situation in which there was no edge strip. When motorists are the only road users on the road, they often occupy space on the road that is not just "their" lane. This means that unlike what was intended, they are not driving farther from the edge of the road than before the introduction of a single lane.

When passing cyclists, motorists are swerving somewhat less to the left since the introduction of the edge strips. This means that the space chosen for use by both motorists and cyclists is less than what should be possible as based on the available space in the cross sectional profile. In other words, they can occupy more space but are not doing so.

It is still too early to conduct an accident analysis of single lane roads but such an analysis will be conducted within a broader framework during a later phase.

Whether or not the carriageway with a single lane on access roads outside urban areas should be introduced into the revised guidelines for the design of non-motorways as a method for marking this type of road is a good question. Previous research findings show that road safety cannot yet be considered as the primary reason for doing so. Apart from this, however, the standardising of what road users perceive on roads of various types is an important reason for emphasising road categorisation. On access roads outside urban areas, cars and bicycles use the same carriageway while travelling at great differences in speed as they pass and meet one another. The recognisability of this situation increases by a marking system that clearly indicates the location for the car (single lane) and the bicycle (edge strip). For this reason, SWOV is currently recommending this kind of marking on all access roads outside of urban areas. The accident study can provide new perspectives later.

SWOV Research Activities 18 - November 2001

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