sources make a distinction between roundabouts and traffic circles,
stating that roundabouts have certain "modern" design elements
such as a yield on entry to circulating drivers, and deflection from a
straight path of approaching vehicles.
roundabout, or traffic circle is contracted at intersections and
requires drivers to circulate to reach their intended exit. One problem
is that if the diameter of the roundabout is less than about 45 feet
large trucks cannot make 270 degree left turns around it. In the UK this
is overcome by making some (small roundabouts) or all (mini-roundabouts)
of the roundabout able to be driven over by the wheels of a truck. In
the UK however drivers are used to circulating roundabouts. In the US
this may lead some drivers to go straight across a roundabout, if it is
physically possible. In fairly low traffic situations roundabouts can
still be used by trucks which will make left turns in front of the
photo of a typical small (approximately 25 feet in diameter) roundabout
is shown below.
can be seen it provides an aesthetic improvement to the road and reduces
the perception of a long straight road. I have used a roundabout in a
temporary form in the US (see photo) on a collector road carrying
approximately 6000 vehicles per day.
intention is to reduce traffic speeds and divert traffic to a parallel
arterial (somewhat as an alternate to speed humps). Two more roundabouts
will be installed on the collector (approximately one third mile in
length) to give a better trial of roundabouts. Therefore at this time I
do not know if they will slow and divert traffic. I am however in favor
of the increased use of roundabouts particularly as an alternative to
four way stops. Their aesthetics (when permanent) and the need to slow
down to negotiate them makes them a useful traffic calming tool.