QUEUING ANALYSIS
GENERAL
 Queue lengths can be determined by the following procedure: 1.25 x Volume = Q Length
 When large intersections are involved or it is known that a cycle length greater then 120 seconds is needed, the procedures described below will be used.
Procedures for determining queue lengths at signalized, and unsignalized intersections:
SIGNALIZED INTERSECTIONS
This procedure can be used at intersections with existing signals and intersections where it is felt a signal may be installed.
 Perform critical lane analysis
 Select Cycle length
 use existing timing if available
 if timing is not available, use the suggested cycle lengths
Recommended Maximum Cycle Lengths
LOS 
2 Phase 
35Phase 
68 Phase 
A
B
C
D
E
F 
90
90
100
120
135
150 
100
100
120
135
150
165 
120
120
135
150
165
180 
NOTE: These cycle lengths are to be used as a guide, knowledge of the intersection may result in using a Higher or lower cycle.
 Use Poisson Distribution Chart/Formula to determine maximum number of vehicles per cycle of a specific movement.
FORMULA:
Avg Veh/Cycle = 
Critical Lane Volume (veh/hr) x Cycle Length(sec.)
3600 (sec/hr)

 Assume a vehicle length of 25 ft.
 Once the average vehicles per cycle (specific movement) is determined, the chart can be used to find the maximum vehicles per cycle for that movement.
 The queue length will be the maximum vehicles per cycle times 25 ft. per vehicle.
 It is noted that the chart ends at an average of 20 vehicles per cycle. In cases where the average number of vehicles per cycle exceeds 20 the following formula can be used to determine the queue length. This formula can also be used in lieu of the chart.
Q. = Avg No. of Veh x 1.4 (Surge Factor) x 25 ft.
POISSON DISTRIBUTION
UNSIGNALIZED INTERSECTIONS
This procedure can be used at isolated intersections where it is felt a signal will not be placed. If there is any chance that a signal may be placed at an intersection, the procedure for signalized intersections should be used.
 Determine the critical gap needed for the movement (from chart) this chart is also found in the 1985 HCM unsignalized intersections. BASIC CRITICAL GAP FOR PASSENGER CARS, SEC
Vehicle Maneuver
and
Type of Control

Average Running Speed, Major Road 
30 MPH 
55 MPH 
Number of Lanes on Major Road 
2 
4 
2 
4 
RT from Minor Road
 STOP
 YIELD

5.5
5.0 
5.5
5.0 
6.5
5.5 
6.5
5.5 
LT from Major Road 
5.0 
5.5 
5.5 
6.0 
Cross Major Road
 STOP
 YIELD

6.0
5.5 
6.5
6.0 
7.5
6.5 
8.0
7.0 
LT from Minor Road
 STOP
 YIELD

6.5
6.0 
7.0
6.5 
8.0
7.0 
8.5
7.5 
Note: If restricted sight distance exists add one second to the gap needed. Where average running speeds are between 30 mph and 55 mph, interpolate.
 Determine average gap between opposing vehicles
Average Gap Opposing Vehicle 3600 sec / (Volume Per/Hour)
 If the average gap is greater than the gap needed for the maneuver the same procedure as signalized intersections can be used with the cycle length equal to the critical gap required (from chart) plus 4 seconds (start up time).
 If the average gap is less than or equal to the gap needed, this maneuver should be analyzed as if a signal were in place.
Average No. of Vehicle
Per Cycle

0.1  0.3
0.4  0.8
0.9  1.3
1.4  1.9
2.0  2.6
2.7  3.2
3.3  3.9
4.0  4.7
4.8  5.4
5.5  6.1
6.2  6.9
7.0  7.7
7.8  8.4
8.5  9.2
9.3  10.0
10.1  10.8
10.9  11.6
11.7  12.4
12.5  13.2
13.3  14.0
14.1  14.9
15.0  15.7
15.8  16.5
16.6  17.3
17.4  18.2
18.3  19.0
19.1  19.8
19.9  20.0
Maximum No. of Vehicle
Per Cycle

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28



