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 Signal Timing Design: Professional Practice

 
Critical Movement or Lane

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). . . .