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Sub-problem 2c - Page 2 of 4

ID# C502C02

Sub-problem 2c: Analyzing the Effects of Coordination

Step 2: Results

The arrival type is 3 for all movements under fully actuated control to model random arrivals. This results in a progression factor (HCM Equation 16-10) of 1.00 for all approaches, which means the first term of the delay equation (HCM Equation 16-9) for uniform delay (d1) is not adjusted for coordination.

Under fully actuated control, the HCM procedures account for how responsive an actuated movement reacts to traffic by using the unit extension. This value represents how long (in seconds) a detector must be vacant before the controller will end the phase ("gap out"). In the HCM, the unit extension is used to determine the k-value for use in the delay equation (for incremental delay, d2). So, while fully actuated control does not lower d1, it does lower d2.

Conversely, under semi-actuated control, the reverse is true. Since the major street through movements must be pretimed to accommodate coordination, the arrival type can vary, based on the degree of coordination provided. Under most situations, arrival type 4 is used for normal coordinated systems. (Arrival type 5 could be used in especially well coordinated systems like for one-way streets). Using arrival type 4 for both the eastbound through movement and westbound through and right-turn movements in this case results in progression factors from HCM Exhibit 16-12, based on the green (g/c) ratios but always values less than 1.00 to account for improvements in delay to these movements created by the coordination provided. The progression factor modifies the effects of uniform delay, d1.

However, under semi-actuated control, the unit extension value for the eastbound through movement and the westbound through and right-turn movements will be ignored since these movements are under pretimed operation, resulting in a k-value of 0.50. This will not lower the d2 value, so we have a trade-off between these two control strategies.

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