Traffic Signal Timing Calculator

This calculator walks through the core timing relationships engineers use to evaluate — not design from scratch — a signalized intersection approach. It first computes lost time per phase as the sum of yellow and all-red clearance intervals, multiplies by the number of phases to get total lost time per cycle, and subtracts that from the cycle length to find the effective green time split evenly across phases (a simplification; real intersections rarely split green equally). It then derives an approach's capacity from the saturation flow rate — the maximum vehicles per hour that can pass during continuous green — scaled by the fraction of the cycle that's usable green time, using the base saturation flow rate and adjustment-factor structure set out in the Highway Capacity Manual, 6th Edition (Transportation Research Board), which anchors the default 1,800 vph/lane value here (HCM's ideal base is 1,900 pc/h/ln before adjusting for lane width, turning movements, and heavy vehicles).

Dividing the approach's actual volume by that capacity gives the volume-to-capacity (v/c) ratio, the standard measure of how saturated an approach is; values approaching or exceeding 1.0 signal breakdown conditions. Finally, it estimates average delay per vehicle using a simplified version of Webster's uniform delay formula, which models delay as a function of the green ratio and the (capped-at-1.0) v/c ratio — this is only the uniform-arrival component, not Webster's full formula, so it omits the random-arrival and overflow delay terms that dominate at high v/c ratios and will understate real-world delay for an oversaturated approach. Use it for a first-pass check of green time and v/c ratio, not a substitute for full HCM signalized-intersection analysis or field-calibrated software.