The signal-controller–mode delay adjustment factor, k, accounts for whether the intersection is operating in an actuated or pretimed mode. A value of 0.5 is used for intersections under pretimed control. Given that actuated intersection control usually results in more efficient handling of traffic volumes, k can take on values less than 0.5 to account for this efficiency and resultant reduced delay. For actuated control, k depends upon the v/c ratio and the passage time (an actuated controller setting related to the maximum amount of time the green display can be extended due to a vehicle detector actuation). For the purposes of the example and end-of-chapter problems, pretimed signal control is assumed.
The upstream filtering/metering factor is used to adjust for the effect that an upstream signal has on the randomness of the arrival pattern at a downstream intersection. An upstream signal will typically have the effect of reducing the variance of the number of arrivals at the downstream intersection. I is defined as
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= variance of the number of arrivals per cycle mean number of arrivals per cycle