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Sub-problem 3a - Page 8 of 9

ID# C103A08

Sub-problem 3a: Oversaturated Intersection Analysis

Exhibit 1-32 shows both the initial and revised demands for time period 3 (4:30 - 4:45 pm):

Exhibit 1-32. Service Volumes vs. Demand Volumes at Styner-Lauder under Signal Control (4:30 - 4:45 pm)
Time
Period		 Eastbound Westbound Northbound Southbound
LT TH RT LT TH RT LT TH RT LT TH RT
Initial demand (veh/hr), time period 3 45 60 175 55 85 150 20 1,015 45 50 1,350 130
Excess demand from time period 2   6 28       88       54 5
Final demand (veh/hr), time period 3 45 66 203 55 85 150 108 1,015 45 50 1,405 135

For this analysis, we will use the initial demand. In addition, we will use the excess demand as the initial queue, or unmet demand, that is one of the required parameters in the computation of control delay in the HCM Chapter 16 procedure. The results of this analysis, for time period 3 (4:30 - 4:45 pm), are shown in Exhibit 1-33:

Exhibit 1-33. Lane Group Capacity, Control Delay, and LOS Determination at Styner-Lauder under Signal Control (4:30 - 4:45 pm) (Dataset17)
Approach EB WB NB SB
Movement LT TH/RT LT TH/RT LT TH/RT LT TH/RT
Adj flow rate 45 235 55 235 20 1,060 50 1,480
Lane group capacity 257 422 257 430 149 2,097 247 2,082
v/c ratio 0.18 0.56 0.21 0.55 0.13 0.51 0.20 0.71
Green ratio 0.25 0.25 0.25 0.25 0.58 0.58 0.58 0.58
Control delay 19.1 31.9 19.7 24.5 193.5 8.3 5.5 9.5
Lane group LOS B C B C F A A A
Approach delay 29.9 23.6 11.7 9.4
Approach LOS C C B A
Intersection delay 13.3 Intersection LOS B

The unserved demand that was present at the end of time period 2 (4:15 - 4:30 pm) was successfully served during time period 3 (4:30 - 4:45 pm). The delay for the NB LT movement is still quite high, but all volume/capacity ratios are less than 1.0. Therefore, the analysis of the effects of oversaturation can be considered to be complete.

It is worth noting that the control delay reported in Exhibit 1-33 includes the additional delay experienced by vehicles in the residual queue that was transferred to time period 3 from time period 2. The HCM procedure accounts for the carryover of excess demand through the third (d3) term of the delay equation.

We  will still want to analyze the last 15-minute time period in order to determine the average control delay for the hour, and this is done on the next page.

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