Once you have the total cycle length, you can determine the length of time that is available for green signal indications by subtracting the intergreen periods from the total cycle length. But, the result is useless unless you know how to allocate it to all of the phases of the cycle. 

As explained in the module about critical movement analysis, the critical movements or lanes are used to distribute the available green time among all of the phases. The flow ratio for a movement or lane is the actual (design) flow rate, for that entity, divided by the saturation flow rate. The critical flow ratio, which is the one that is important for this calculation, is the flow ratio for the critical movement or lane. 

Green time is allocated using a ratio equation. Each phase is given a portion of the available green time that is consistent with the ratio of its critical flow ratio to the sum of all the critical flow ratios. This calculation is simple to do and hard to say, which makes it refreshingly different from most of the other calculations we encounter in engineering.