Sub-problem 2c - Page 2 of 4
Analyzing the Effects
Step 2: Results
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
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.
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
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