Example data table
| Scenario | Cycle C (s) | Phases | Total lost L (s) | Effective green G (s) | Example green split outcome |
|---|---|---|---|---|---|
| Urban 4‑leg peak | 90 | 4 | 16 | 74 | Phase greens allocated by y=v/s; busiest approach gets the largest share. |
| Work zone detour | 110 | 3 | 15 | 95 | User-defined percentages scaled to effective green for quick field tuning. |
| School crossing | 80 | 2 | 10 | 70 | Custom green seconds capped to available effective green for safety timing. |
Formula used
Effective green available: G = C − L
Where C is cycle length and L is the sum of phase lost times.
Flow ratio per phase: yᵢ = vᵢ / sᵢ
Volume vᵢ is the demand and sᵢ is the saturation flow.
Green split allocation: gᵢ = (yᵢ / Σy) × G
This assigns more green to phases with higher critical demand.
Split percent of cycle: Splitᵢ(%) = (gᵢ / C) × 100
How to use this calculator
- Set the cycle length to match your corridor plan.
- Choose the allocation method that fits your workflow.
- Enter lost time for each phase based on controller settings.
- For proportional allocation, enter volumes and saturation flows.
- For user-defined mode, enter split percentages or green seconds.
- Click calculate to see results above the form.
- Export the latest run using the CSV or PDF buttons.
Professional article
Green split design converts a cycle length into phase times. On construction projects, traffic patterns can change daily because of lane shifts, haul‑truck access, temporary signing, and reduced approach widths. A consistent green‑split workflow helps supervisors justify timing decisions, keeps queues predictable, and reduces conflict near work areas.
Start with a realistic cycle length for the intersection and corridor. Shorter cycles reduce delay for side streets and pedestrians, while longer cycles can improve capacity for dominant movements. Next, estimate lost time for every phase. Lost time includes startup and clearance effects that reduce the portion of the cycle that actually serves vehicles. The calculator sums phase lost times (L) and computes effective green (G = C − L). Effective green is the only time available to distribute.
Use flow‑ratio allocation when you have demand and capacity inputs. For each phase, compute the flow ratio y = v/s, where v is the hourly demand and s is the saturation flow under site conditions. Work zones often lower saturation flow because of narrow lanes, reduced speeds, heavy vehicles, and tight turning paths, so use field‑based values when possible. The calculator allocates green as gᵢ = (yᵢ/Σy)×G. Phases with higher critical demand receive more green, which usually improves queue balance and reduces spillback risk.
Use user‑defined allocation when an approved timing plan already exists or when quick adjustments are needed during staging. You may enter split percentages or green seconds. Inputs are scaled to match effective green so total greens do not exceed what the cycle can provide. This makes it easier to compare planned versus required splits and communicate changes to the controller technician.
Example data: choose C = 90 s with four phases, each with 4 s lost time. Total L = 16 s, so G = 74 s. If measured demands are v = [650, 520, 430, 360] veh/h and saturation flow is 1900 veh/h for each approach, then y = v/s gives the highest weight to Phase 1. The resulting green allocation will favor Phase 1, then Phase 2, helping the busiest approach clear within each cycle.
After computing splits, verify in the field. Watch whether queues fully discharge, whether pedestrians receive minimum service, and whether heavy vehicles block turning paths. Recheck after any stage change or shift in peak direction. Accurate splits support safer, smoother traffic control operations throughout the project day for crews on site.
FAQs
1) What is “effective green” in this calculator?
Effective green is the cycle time available for serving vehicles after subtracting total lost time. The calculator uses G = C − L to allocate green fairly and keep totals consistent with your phase change losses.
2) Should I include yellow and all-red in lost time?
Lost time represents startup and clearance effects. If your yellow and all-red are already accounted for in your phase lost time assumptions, include them. Otherwise, treat yellow/all-red as controller intervals and keep lost time as operational loss.
3) What saturation flow value should I use in a work zone?
Use a realistic value reflecting lane width, grade, heavy vehicles, turning radius, and temporary channelization. When uncertain, start conservative and refine with short field observations or project guidance to avoid under-allocating green.
4) My split percentages do not add to 100%. Is that okay?
Yes. In user-defined percentage mode, the tool scales positive entries to the available effective green, then reports the resulting split as a percent of the full cycle. This keeps calculations usable during quick planning.
5) Why does the last phase change slightly after rounding?
Rounding can make the sum of phase greens drift away from effective green. The calculator adjusts the final phase by the small difference so the rounded greens still match G and remain controller-friendly.
6) Can this be used for pedestrian timing?
It can support planning, but pedestrian requirements need separate checks for walk and clearance times. Ensure each pedestrian-served phase meets minimums before accepting the computed green, especially near schools or detour crossings.
7) Does a good green split guarantee good progression?
No. Progression depends on offsets, spacing, and travel speeds. Use this tool to get a balanced split first, then confirm offsets and bandwidth with your corridor plan or signal timing software.
Accurate green splits improve flow, safety, and daily operations.