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T.P.D.M.V.2.4
(Al/2001)
Table 4.2.9.1
Factors Affecting Choice of Junction Type
Design Parameter
Priority Junction
Traffic Signal Junction
Roundabout Junction
Grade Separated Junction
CAPACITY
Low - moderate flows
Moderate - high flows Moderate - high flows
High flows
DELAY
At top end of flow range long
delays experienced by minor
road traffic
Adjacent junctions can be linked
to minimise delay. However
unnecessary delay unavoidable
during most quiet hours even
with minimum cycle time
Little delay if capacity not
exceeded
No delay to major through
traffic. Little or no delay to
minor turning movements
SAFETY
Relies heavily on driver
judgement and is susceptible to
accidents at top end of flow
range
Low right turn and pedestrian
accident rate but may cause high
rear end accident rate especially
on high speed roads
Generally the safest form of atgrade
junction over a wide range
of flows and speeds
Some or all conflicting
movements are removed with a
consequent decrease in number
of accidents. The few accidents
which do occur may be severe
owing to high speeds
ECONOMIC
CONSIDERAT-
IONS
Very low construction costs, but
land take may be costly for
larger physical island
channelized junctions
Generally very cost effective.
Cost of equipment is offset by
reduction in land take
May be extravagant in terms of
land take and consequently
expensive. However check
small and mini roundabout
designs
Construction costs are high but
these should be offset against
reduction in community costs
through fewer accidents, less
delay etc. G.S.I.'s can also be
economic users of land
PEDESTRIAN
CONSIDERAT-
IONS
Small simple junctions and
those with physical
channelisation may adequately
cater for pedestrian demand.
Shadow islands however should
be avoided if pedestrian flow is
heavy
Pedestrians can generally be
catered for better at signals than
at other at-grade junctions
through positive indication
Pedestrian routes through
roundabout junctions may be
diverse and unattractive.
Subways and/or footbridges
should be considered for heavy
pedestrian demand
Grade separated pedestrian
facilities required