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Sub-problem 3a - Page 7 of 9

ID# C103A07

Sub-problem 3a: Oversaturated Intersection Analysis

The results for the second 15-minute time period (4:15 pm to 4:30 pm) are shown in Exhibit 1-30:

Exhibit 1-30. Lane Group Capacity, Control Delay, and LOS Determination at Styner-Lauder - Signal Control (4:15-4:30 pm) (Dataset16)
Approach EB WB NB SB
Movement LT TH/RT LT TH/RT LT TH/RT LT TH/RT
Adj flow rate 50 450 55 205 215 1,075 59 2,140
Lane group capacity 283 416 127 432 127 2,091 240 2,081
v/c ratio 0.18 1.08 0.43 0.47 1.69 0.51 0.25 1.03
Green ratio 0.25 0.25 0.25 0.25 0.58 0.58 0.58 0.58
Control delay 19.0 90.3 29.3 22.9 355.8 8.3 6.2 35.0
Lane group LOS B F C C F A A D
Approach delay 83.2 24.2 66.2 34.3
Approach LOS F C E C
Intersection delay 49.1 Intersection LOS D

The increase in traffic flow rates during this second time period results in a much poorer performance at the intersection. The major thing to point out from Exhibit 1-30 is that the volume/capacity ratio for three lane groups exceeds 1.0.

What is the practical implication of this result? The excess demand for each of these lane groups (that is, the difference between the lane group capacity and the adjusted flow rate) is transferred to the next time period (4:30 pm to 4:45 pm). The excess demand is shown in Exhibit 1-31. Note that since the demand is shown first in vehicles/hour that we also show the actual number of vehicles that would be transferred to the next time period.

Exhibit 1-31. Excess Demand at Styner-Lauder under Signal Control (4:15-4:30 pm)
Approach EB WB NB SB
Movement LT TH/RT LT TH/RT LT TH/RT LT TH/RT
Adj flow rate 50 450 55 205 215 1,075 59 2,140
Lane group capacity 283 416 127 432 127 2,091 240 2,081
Excess demand (veh/hr)   34     88     59
Excess demand (vehicles)   9     22     15

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