Effective green time is the time during which a given traffic movement or set of movements may proceed at saturation flow rate; it is equal to the cycle length minus the effective red time. Stated another way it is g = G + Y - Lost Time, where lost time includes start-up delay and a portion of the yellow that is not utilized.

The graphic above illustrates effective green time. Effective green time excludes start-up delay that occurs at the beginning of the phase as well as any lost time that might occur near the end of the phase.