Work out saturation flow rate instantly with clear inputs, formula shown and shareable results.
Saturation flow is the maximum discharge rate from a signal stop line once the queue is moving, about 1900 PCU per hour per lane under ideal conditions. Adjustment factors reduce it for narrow lanes, uphill approaches and turning movements, which take longer to clear because drivers must judge gaps or negotiate a smaller radius.
Adjusted saturation flow
s = base saturation x width factor x gradient factor x turning factor
s = base saturation x width factor x gradient factor x turning factor. Saturation flow is the maximum discharge rate from a signal stop line once the queue is moving, about 1900 PCU per hour per lane under ideal conditions.
Yes where possible. Measured discharge headways at the site are far more reliable than factored defaults, because local driver behaviour dominates.
This calculator takes 4 inputs: Base saturation flow per lane, Lane width, Approach gradient, Share of turning movements. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.