Intersection Inputs
Use the responsive form below. Large screens show three columns, smaller screens show two, and mobile shows one.
Example Data Table
This sample illustrates a four-phase intersection during peak demand.
| Phase | Movement | Demand Volume (veh/h) | Saturation Flow per Lane | Lanes | Pedestrian Constraint |
|---|---|---|---|---|---|
| 1 | Northbound through/right | 620 | 1900 | 1 | 12 s |
| 2 | Southbound through/right | 480 | 1850 | 1 | 12 s |
| 3 | Eastbound through/right | 710 | 1900 | 1 | 10 s |
| 4 | Westbound through/right | 530 | 1800 | 1 | 10 s |
Formula Used
1. Adjusted demand volume: vadj = v / PHF
2. Critical flow ratio: yi = vadj / (s × lanes), and Y = Σyi
3. Total lost time: L = n × (startup lost + amber + all-red)
4. Webster optimum cycle: C₀ = (1.5L + 5) / (1 - Y)
5. Effective green split: gi = (yi / Y) × (C - L), then pedestrian and minimum green constraints are applied.
6. Phase capacity: ci = s × lanes × (gi / C)
7. Degree of saturation: X = vadj / ci
8. Uniform control delay: d = 0.5C(1 - g/C)² / (1 - min(1, X) × g/C)
9. Queue estimate: Queue ≈ (vadj / 3600) × d
This model is best for planning-level optimization. Field observations, detector tuning, turning shares, progression bands, and local standards should refine final timings.
How to Use This Calculator
- Enter the peak hour factor and analysis period.
- Input lost time, amber, all-red, and minimum green settings.
- Set pedestrian minimums for north-south and east-west crossings.
- Provide demand volume, saturation flow, and lanes for each phase.
- Choose a practical maximum cycle length for your project.
- Click Optimize Signal Timing to generate the result block above the form.
- Review cycle length, phase greens, delay, queue, and LOS.
- Download the results as CSV or PDF for reporting.
Frequently Asked Questions
1. What does this calculator optimize?
It estimates a practical cycle length and allocates green time among four phases. The model also reports delay, queue, capacity, v/c ratio, and level of service for each phase.
2. Which timing method is used?
The calculator uses Webster-style cycle optimization and proportional green splits. It then applies minimum green and pedestrian constraints before computing phase capacity and uniform delay.
3. Why is peak hour factor included?
Peak hour factor adjusts hourly demand for short-term traffic concentration. Lower values represent stronger peaking, which raises adjusted demand and often increases the optimized cycle length.
4. What happens if the flow ratio is too high?
If the total critical flow ratio approaches one, the intersection becomes unstable. The calculator warns you because timing alone cannot reliably serve demand without added capacity or reduced arrivals.
5. Are pedestrian needs considered?
Yes. The calculator applies separate pedestrian minimum greens for north-south and east-west phases. If these constraints exceed available effective green, the cycle is increased within the allowed maximum.
6. Is the delay result suitable for final signal plans?
Use it for planning, screening, and option comparison. Final designs should also check coordination, turn pockets, detector settings, heavy vehicles, local warrants, and field performance.
7. Can I export the outputs?
Yes. You can download the optimized result table as CSV or PDF. The example dataset can also be exported as CSV for quick testing.
8. How should I interpret LOS?
LOS converts average control delay into an operating grade from A to F. Lower delay indicates smoother operation, while high delay suggests congestion, poor splits, or oversaturation.