Traffic Signal Cycle Length Calculator

Example Data Table

Formula Used

Adjusted flow: v = V / (PHF × fHV)

Heavy vehicle factor: fHV = 1 / [1 + PT × (ET - 1)]

Critical flow ratio: y = v / s

Total critical ratio: Y = y1 + y2 + y3 + y4

Webster cycle: C = (1.5L + 5) / (1 - Y)

Green split: gi = available green × yi / Y

Capacity: ci = si × gi / C

Volume capacity ratio: X = v / ci

Uniform delay estimate: d = 0.5C(1 - g/C)² / [1 - X(g/C)]

How to Use This Calculator

Enter the number of active signal phases first. Add demand flow for every phase. Use hourly traffic volume values. Enter saturation flow per lane. Add lane count, peak hour factor, heavy vehicle share, and minimum green time.

Use pedestrian walk and flashing time when a phase serves crossings. Add yellow time, all-red time, start-up lost time, and clearance lost time. Leave manual cycle as zero to use the computed cycle. Press the calculate button. Review the cycle, green splits, capacity, delay, and queue estimates.

Traffic Signal Cycle Length Planning

Purpose

A traffic signal cycle length calculator helps estimate a practical timing plan for an intersection. The cycle length is the time needed for every active signal phase to run once. A good cycle should serve traffic demand without wasting green time. It should also protect pedestrians and allow safe clearance between conflicting movements.

Why Cycle Length Matters

Short cycles reduce waiting time when traffic is light. They also help pedestrians get service more often. Long cycles can move more vehicles when traffic is heavy. Yet very long cycles can create large queues. They can also increase delay for minor approaches. The best value balances flow, safety, and available capacity.

Critical Flow Ratio

The calculator uses critical flow ratio as the main demand measure. This ratio compares adjusted traffic demand with saturation flow. A high value means a phase needs more green time. The sum of all critical ratios shows how busy the intersection is. When this sum approaches one, the junction becomes unstable.

Lost Time and Clearance

Signal timing must include time that is not fully usable. Start-up lost time happens when drivers react at the start of green. Clearance lost time covers the end of the phase. Yellow and all-red intervals are kept separate for practical timing. These values affect the final cycle and available green time.

Green Split Design

Green time is divided according to each phase demand. Larger critical ratios receive larger shares. The calculator also checks minimum green and pedestrian time. This prevents a phase from receiving an unsafe or unusable value. If the minimum times need more space, the cycle is increased.

Capacity and Delay Review

After calculating green time, the tool estimates phase capacity. It compares adjusted demand with capacity to produce a v/c ratio. It also estimates average control delay and a simple queue value. These results help planners find weak phases. A high v/c ratio suggests extra green time, lane changes, or demand management.

Practical Use

This calculator is useful for planning, teaching, and early design checks. It does not replace field observation. Real signals may need detector settings, coordination offsets, pedestrian rules, and local standards. Always review the output with traffic counts and safety requirements before using it in the field.

FAQs

What is traffic signal cycle length?

It is the total time required for all active signal phases to run once. It includes green, yellow, and all-red intervals.

What is Webster cycle length?

Webster cycle length is a common signal timing estimate. It uses total lost time and the sum of critical flow ratios.

What is critical flow ratio?

It compares adjusted demand flow with saturation flow. Higher values need more green time because demand is stronger.

Why is lost time important?

Lost time reduces usable green time. It includes driver reaction, start-up delay, and clearance effects between signal phases.

What does v/c ratio mean?

The v/c ratio compares demand volume with available capacity. Values near one show that a phase is close to capacity.

Can this calculator handle pedestrians?

Yes. Enter walk and flashing do not walk time. The calculator uses them as minimum green constraints for that phase.

What happens if Y is above one?

The intersection is oversaturated. Demand is higher than practical signal capacity, so the tool shows a warning instead.

Is the result ready for field use?

Use it as a planning estimate. Field timing should also consider local standards, detector settings, coordination, queues, and safety checks.