Doing Business Access Permit

Guidelines for Traffic Impact Report/Studies

APPENDIX 2

QUEUING ANALYSIS

• 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.

SIGNALIZED INTERSECTIONS

This procedure can be used at intersections with existing signals and intersections where it is felt a signal may be installed.

1. Perform critical lane analysis
2. 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         3-5 Phase       6-8 Phase
   
   A       90              100             120
   B       90              100             120
   C       100             120             135
   D       120             135             150
   E       135             150             165
   F       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.
3. Use Poisson Distribution Chart/Formula to determine maximum number of vehicles per cycle of a specific movement.

FORMULA:

                ritical Lane Volume (veh/hr) x Cycle Length(sec.)
Avg Veh/Cycle =           --------------------------------------------
                           3600 (sec/hr)

1. Assume a vehicle length of 25 ft.
2. 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.
3. The queue length will be the maximum vehicles per cycle times 25 ft. per vehicle.
4. 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

    Average No. of Vehicle       Maximum No. of Vehicle
          Per Cycle                              Per Cycle
        -----------------------                     ---------------------
        0.1 - 0.3                     1
        0.4 - 0.8                       2
        0.9 - 1.3                       3
        1.4 - 1.9                       4
        2.0 - 2.6                       5
        2.7 - 3.2                       6
        3.3 - 3.9                       7
        4.0 - 4.7                       8
        4.8 - 5.4                       9
        5.5 - 6.1                       10
        6.2 - 6.9                       11
        7.0 - 7.7                       12
        7.8 - 8.4                       13
        8.5 - 9.2                       14
        9.3 - 10.0                      15
        10.1 - 10.8                     16
        10.9 - 11.6                     17
        11.7 - 12.4                     18
        12.5 - 13.2                     19
        13.3 - 14.0                     20
        14.1 - 14.9                     21
        15.0 - 15.7                     22
        15.8 - 16.5                     23
        16.6 - 17.3                     24
        17.4 - 18.2                     25
        18.3 - 19.0                     26
        19.1 - 19.8                     27
        19.9 - 20.0                     28

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.

1. 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 Average Running Speed, Major Road
         and 30 MPH          55 MPH

   Type of Control Number of Lanes on Major Road

             2       4       2       4
   
   RT from Minor Road
      STOP            5.5     5.5     6.5     6.5
      YIELD                5.0     5.0     5.5     5.5
   
   LT from Major Road      5.0  5.5     5.5     6.0
   
   Cross Major Road
      STOP              6.0     6.5     7.5     8.0
      YIELD                5.5     6.0     6.5     7.0     

   LT from Minor Road
      STOP              6.5     7.0     8.0     8.5
      YIELD                6.0     6.5     7.0     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.

    

2. Determine average gap between opposing vehicles
   Average Gap Opposing Vehicle   3600 sec / (Volume Per/Hour)
   
3. 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).
4. 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.

      No Lanes        Factor
        1             1.00
        2               .55
        3               .40
        4               .30
        DBL L.T         .60