Civil Engineering Reference
In-Depth Information
16.6 Intersection Turn Controls and Management
Left and right turns impede traf
”
is usually critical in areas of heavy pedestrian activity commonly found in the city
center and in older high-density neighborhoods.
Left turns, however, create intersection delays throughout the street system.
They con
c
fl
flow at many locations. The
“
right-turn problem
fl
ict with opposing through traf
c, can also block vehicles behind them
and complicate traffic signal phasing.
To reduce intersection delay many urban areas restrict left and right turns. These
restrictions preserve capacity and reduce congestion, and can be in effect all day
(7 a.m. to 7 p.m.) or just during rush hours.
Managing left and right turns at busy intersections by restriction or rerouting, is a
long established and cost-effective way to reduce delays and congestion at busy
intersections. Prohibiting left turns permits fewer phases, shorter cycle lengths, and
longer
“
green times
”
for the through movement. This translates into more capacity
and less delay.
16.6.1 Managing Right Turns
Right turn restrictions are sometime needed on intersection approaches where
both
right turns and pedestrian volumes are heavy. These restrictions result into shorter
cycle lengths and reduce delays.
The travel times gained by
restricting right turns
can be estimated by applying
the following equation [
16
]:
t
s
L
t
¼
r
p
ð
16
1
Þ
D
:
where
D
t green time to be gained per cycle
r
right turns/cycle (peak 15 min)
p
con
fl
icting pedestrians per cycle (peak 15 min)
t
s
time loss per pedestrian (e.g., 3
-
4 s), and
L
number of pedestrian channels in crosswalk
Using the above equation, the amount of time lost due to right turns and
pedestrian conflicts can be estimated. The estimated times lost per signal cycle for a
range of con
icting right turns and pedestrian volumes is shown in Table
16.4
.
For example, if there are 300 pedestrians per hour con
fl
icting with 240 right
turns per hour (@ 60 cycles/h: 5 pedestrians and 4 right turns per cycle), and 3 s lost
per con
fl
fl
ict, about 20 s per cycle would be lost, assuming 3 pedestrian channels, or
20 = (4)
×
(5)
×
(3)/3.
