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T.P.D.M.V.2.4
*J.5.7
Safety at Roundabouts
4.5*7.1 In general a well designed roundabout will cause fewer accidents
than a signal controlled junction handling the same volume of
traffic. The severity of accidents at roundabouts is also lower
than that of all other junction types and mid link locations.
4.5.7.2 The most important factor affecting safety at roundabouts is the
entry and circulatory speeds. High speeds are normally
associated with large roundabouts having excessively long and/or
wide circulatory carriageways, but they can also be caused at
smaller roundabouts by inadequate entry deflection. Other
factors inducing high speeds at roundabouts include : very acute
entry angles which encourage fast merging, poor visibility to
the "Give Way* line and poorly designed and located warning and
advanced direction signs.
4.5.7.3 Measures which have been found to improve safety at roundabouts
include, the provision of appropriate levels of skid resistance
on the approaches an circulatory carriageway; the avoidance of
abrupt and excessive super-elevation in the entry region; the
reduction of excessive entry width by hatching or physical
means; and the provision of "Reduce Speed Now 11 signs and "Yellow
Bar" markings on the approaches* Volume 3 Chapter 5 gives
detailed information on the use of "Yellow Bar* markings.
4.5.7.4 Though roundabouts have an impressive overall safety record for
most vehicle types this does not apply equally to two wheeled
vehicles. Statistics from the United Kingdom show that accident
involvement rates for two-wheeled vehicles, expressed in terms
of accidents per road user movement, are 10-15 times those of
cars; with pedal cyclists having a slightly higher accident rate
than motor cyclists. It is useful to note that different types
of roundabouts exhibited different results in this respect. For
example, normal roundabouts with small central islands and
flared entries have accident rates which are about twice those
of normal roundabouts with large central islands and unflared
entries. This relationship appears to apply consistently for
all types of vehicle,
4.5.7.5 Heavy goods vehicle accidents at roundabouts frequently involve
the shedding of loads. Roundabouts, where this problem has been
encountered usually exhibit one or more of the following
features : inadequate entry deflection, long straight sections
of circulatory carriageway, sharp turns into exits, excessive
orossfall changes on the circulatory carriageway and excessive
adverse orossfall on a nearside lane of the circulatory
carriageway.