The analysis and evaluation of signalized intersections, including most planning tasks, proceed on a lane-by-lane basis. Not all the lanes, however, are equally important. Normally, in every phase there is only one lane for which the relationship between the arrival flow and saturation flow results in the longest green interval requirement. Such lanes are called critical lanes. The number of critical lanes equals the number of phases in a cycle and, together, they have a decisive influence on the cycle time.
A critical lane can be recognized by the highest flow ratio in a given phase:
ycrit j = max (yij) = max (qij /Sij)