At a signalised intersection, vehicles arriving during the red interval accumulate in a queue. The length of this queue depends on how many vehicles arrive, how quickly they can be discharged during the green interval, and the timing characteristics of the signal cycle.
Key variables that influence queue length are the approach flow rate (q), the saturation flow rate per lane (s), the number of lanes (n) serving the movement, the effective green time (g), and the total cycle length (C). The degree of saturation X = q/(s·n) captures the proportion of the available discharge capacity that is being used.
The maximum queue length (in vehicles) can be estimated with a simple linear model that multiplies the degree of saturation by the red‑time portion of the cycle and scales it to an hourly basis. This provides a quick engineering check for signal timing plans.
X = degree of saturation = frac{q}{s,n}
q = approach flow rate (veh/h)
s = saturation flow rate per lane (veh/h/ln)
n = number of lanes
g = effective green time (s)
C = cycle length (s)
How do I calculate the queue length for a single lane?
What does saturation flow rate mean in this context?
How does increasing the number of lanes affect queue length?
What is the impact of a longer effective green time on queue length?
How does the total cycle length affect queue formation?
Can you explain what approach flow rate means in this context?
How do I adjust the formula if some lanes are reserved for turning movements?
Results are for informational purposes only and do not constitute professional advice.