The following excerpt was taken from the 1995 Canadian
Capacity Guide for Signalized Intersections, Second Edition, published by the
Institute for Transportation Engineers (District 7 - Canada), (p. 46.)
Critical Lanes
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)
Where:
ycrit j = flow ratio for the critical lane in phase j
yij = flow ratio for lane i in phase j
qij = arrival flow in lane i discharging in phase j (pcu/h)
Sij = saturation flow in lane i discharging in phase j (pcu/h). . . .