Policy instruments (3) - Transport Policy and Planning in Great Britain - page 223

buses or for vehicles requiring access to frontage properties. Otherwise a standard set
of exemptions is normally applied for emergency and utility vehicles.
Restrictions on turning movements at junctions may need to be imposed in order
to complement traffic restrictions operating in the streets to which they give entry.
They may also be introduced to alleviate safety or congestion problems at the junction
itself. In two-way streets the presence of significant flows of right-turning traffic is
particularly problematic. The potential conflict this represents with oncoming traffic
is hazardous. This can be alleviated at signal-controlled junctions by the provision of a
separate right-turning phase, although usually at the expense of overall traffic capacity.
Unless the width of the carriageway allows for a separate lane the presence of queuing
right-turning vehicles also reduces the throughput of vehicles travelling straight
ahead. This situation may be overcome by banning the right-turn and displacing the
turning movement via alternative routes before or after the principal junction instead.
Exemptions to the ban are likely to be needed for buses in order to avoid extending
route-lengths and bypassing important stopping points.
Conflicts associated with right-turning vehicles are one of the principal reasons
for introducing one-way systems in congested urban locations where the nature and
configuration of streets is suitable. Instead of a series of prohibited turns, traffic is
directed instead to follow a mandatory pattern of movement (using blue arrow signs).
One-way systems can achieve better traffic utilisation of available carriageway space
but have the disadvantage, partly through higher speeds, of making pedestrian crossing
more difficult. Unless special arrangements are made for buses (e.g. by use of contra-
flow lanes) these systems are also likely to reduce accessibility to key destinations.
Within streets the marking of the carriageway into separate lanes, although only
advisory, is a core feature of contemporary practice. It is especially important at the
approaches to intersections in order to segregate the different turning movements and,
in conjunction with the phasing of traffic lights, to maximise the traffic throughput
and/or to allow opportunities for protected pedestrian crossing or public transport
priority movements on other arms of the junction.
Mandatory regulation may restrict certain lanes to particular classes of user, most
commonly with-flow bus lanes at the kerbside. Typically these are introduced as a
way of enabling buses to bypass other traffic which is queuing back from a congested
junction or other restriction on the highway. Bus lanes are normally terminated short
of a signalised junction so that the full approach width is available as a reservoir for
all traffic to use in the next green phase in the cycle. Signals acting as 'bus gates' can
also be used to give buses preferential access into constricted sections of road where
continuation of a bus lane is not possible.
In principle it is possible to expand the utilisation of bus lanes by making them
available to other classes of vehicle without significantly undermining their prime
objective. The most likely additional category (allowed for in some places) is taxis.
However because the private hire vehicle variety is virtually indistinguishable from
ordinary cars this can create the impression that infringement is taking place, inviting
other motorists to follow and thereby causing enforcement problems.
A similar objection might apply to the inclusion of cars with more than one
occupant - creating 'high occupancy vehicle' (HOV) lanes. Nevertheless in the
interests of improving the economic performance of bus lanes this is an option
which highways authorities have been recommended to consider (DfT 2006d).
Remarkably (in view of their apparent merits and extensive use in other countries)
there have only been three examples of HOV lanes in Britain, the most recent being