# Effective Green and Red

Effective Green and Red Times For analysis purposes, the time during a cycle that is effectively (or not effectively) utilized by traffic must be used rather than the time for which green, yellow, and red signal indications are actually displayed, because they are most likely different. This results in two measures of interest: the effective green time and the effective red time. The effective green time is the time during which a traffic movement is effectively utilizing the intersection. The effective green time for a given movement or phase is calculated as

Lg G Y AR t= + + − (7.3)

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where

g = effective green time for a traffic movement in seconds, G = displayed green time for a traffic movement in seconds, Y = displayed yellow time for a traffic movement in seconds,

AR = displayed all-red time in seconds, and tL = total lost time for a movement during a cycle in seconds. The effective red time is the time during which a traffic movement is not

effectively utilizing the intersection. The effective red time for a given movement or phase is calculated as

Lr R t= + (7.4)

where

r = effective red time for a traffic movement in seconds, R = displayed red time for a traffic movement in seconds, and tL = total lost time for a movement during a cycle in seconds.

Alternatively, the effective red time can be calculated as follows, assuming that the cycle length and effective green time have already been determined:

r C g= − (7.5)

where

C = cycle length in seconds, and other terms are as defined previously.

Likewise, the effective green time can be calculated by subtracting the effective red time from the cycle length. Capacity Because movements on an intersection approach do not receive a constant green indication (as assumed in the definition for saturation flow rate), another measure must be defined that accounts for the hourly volume that can be accommodated on an intersection approach given that the approach will receive less than 100% green time. This measure is capacity and is given by

c = s × g/C (7.6)

where

c = capacity (the maximum hourly volume that can pass through an intersection from a lane or group of lanes under prevailing roadway, traffic, and control conditions) in veh/h,

s = saturation flow rate in veh/h, and g/C = ratio of effective green time to cycle length.