Trafiksikkerhed i rundkørsler i Danmark - Cykelviden

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Trafiksikkerhed i rundkørsler i Danmark - Cykelviden

more used to roundabouts in general or it may be that the illumination has become better.

The analyses can not give the answer.

An important reason for this study has been to throw light on the effects of the geometric

layout on roundabout safety. The effects of a speed reducing layout of the approaches

is illustrated by means of a study of single vehicle accidents in the approaches.

A theoretical parameter called "Expected entry speed" or just "Entry speed"

is used as a measure for the degree of speed reduction due to the geometrical layout.

There are indications in the data that a fairly narrow entry - i.e. strong speed reduction

or low "expected entry speed" - lead to increased accident rates in rural areas (80 km/h

zone) while the entry speed is of marginal importance in urban areas (50 km/h zone).

This dependence on "expected entry speed" is related to single vehicle accidents only

and not to accidents between entering versus circulating vehicles. One hypothesis to

explain this observation could be that road users' selected speed at the entry is influenced

more by the general speed level in the surrounding road network than by the

geometry at the entry. However, speed measurements at a number of roundabout entries

indicate that the speeds of freely moving vehicles are about the same in urban and

in rural areas - about 30 km/h at the give way line - and speeds do not depend on the

geometry measured in terms of the "expected entry speed". So far, this problem remains

unsolved.

Cycle facilities either as a cycle track separated by a curb along the circulation area or

as a cycle lane separated by a line marking has been compared with no cycle facilities

in the roundabout. No significant differences have been found.

The width of the circulation area has no effect on accident rates. This also applies to

the diameter of the central island although there is an insignificant tendency to larger

accident rates at large diameters (> 30 m).

Accident rates for roundabouts have been compared to accident rates for signalised intersections.

The comparisons are based on Danish regression models for accident

numbers at signalised intersections. It is concluded that on average roundabouts will

have slightly fewer accidents than signalised intersections having the same traffic

flows. However, differences are small so that a general recommendation of roundabouts

in stead of signalised intersection from a safety point of view may not be given.

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