Highway Capacity Manual 2000
Chapter 16 - Signalized Intersections
16-38
Example Problems
EXAMPLE PROBLEM 1
The Intersection
The intersection of Third Avenue (NB/SB) and Main Street (EB/WB)
is located in the central business district (CBD) of a small urban area.
Intersection
geometry and flow characteristics are shown on the Input Worksheet.
The Question
What are the delay and peak-hour LOS of this intersection?
The Facts
√
EB and WB HV = 5 percent,
√
Third Avenue has two lanes, one in each direction,
√
NB and SB HV = 8 percent,
√
Main Street has four lanes, two in each direction,
√
PHF = 0.90,
√
No parking at intersection,
√
Two-phase signal,
√
Pedestrian volume = 100 p/h, all approaches,
√
NB-SB green = 36 s,
√
Bicycle volume = 20 bicycles/h, all approaches,
√
EB-WB green = 26 s,
√
Movement lost time =
4 s, and
√
Yellow = 4 s,
√
Level terrain.
Comments
√
Assume crosswalk width = 10 ft for all approaches,
√
Assume base saturation flow rate = 1,900 pc/h/ln,
√
Assume E
T
= 2.0,
√
No buses, and
√
70.0-s cycle length, with green times given.
Steps
1.
Pedestrians/cycle.
100
p
h
*
1h
3,600 s
*70s
=
1.944 p
2.
Minimum effective green time
required for pedestrians (
use
Equation 16-2
).
G
p
= 3.2 +
L
4.0
+ 0.27N
ped
G
p
(Main) = 3.2 +
30
4.0
+ 0.27(1.944) = 11.2 s
G
p
(Third) = 3.2 +
44
4.0
+ 0.27(1.944) = 14.7 s
3.
Compare minimum effective
green time required for
pedestrians with actual
effective green.
G
p
(Main) = 26 s, which is >11.2 s
G
p
(Third) = 36 s, which is >14.7 s
4.
Proportions of left and right
turns.
Proportions of left- and right-turn traffic are found by
dividing the appropriate turning volumes by the total
lane group volume.
P
LT
(EB)
=
65
65
+
620
+
35
=
0.090
5.
Lane width adjustment factor
(
use Exhibit 16-7
).
f
w
=
1
+
(W
−
12)
30
f
w
(EB)
=
1
+
(11
−
12)
30
=
0.967
6.
Heavy-vehicle adjustment
factor (
use Exhibit 16-7
).
f
HV
=
100
100
+
%HV(E
T
−
1)
f
HV
(EB)
=
100
100
+
5(2.0
−
=
0.952
7.
Percent grade adjustment
factor (
use Exhibit 16-7
).
0% grade, f
g
= 1.000