Webster Signal Timing Calculator

Webster isolated undersaturated cycle (1.5L+5)/(1−Σy), effective greens ratio-allocated; no intergreen/pedestrian timing or network recommendation. Caller independently establishes units, regime, calibration and applicability; this does not establish design-code compliance, authenticity, operational safety, treatment efficacy or a validated forecast.

Description

Webster's cycle model relates lost time to independently established critical flow ratios.

Webster's cycle model relates lost time to independently established critical flow ratios.^[1]

Its arithmetic does not establish saturation flows or approve a signal plan. Use this tool to calculate webster Signal Timing from the supplied measurements and assumptions.

When to use Webster Signal Timing Calculator

Use this tool to calculate webster Signal Timing from the supplied measurements and assumptions. Establish the SI units or caller unit basis, load signs, measurement interval, model conditions and independently chosen coefficients or references.

How to use Webster Signal Timing Calculator and understand its results

Establish the SI units or caller unit basis, load signs, measurement interval, model conditions and independently chosen coefficients or references.
Enter callerCriticalFlowRatios, totalLostTimeSeconds, using the field meanings and rules below, then run the tool.
Read websterModeledCycleSeconds, effectiveGreenSecondsByCriticalStage. Interpret the fields using their units, signs and evidence conventions below.
If input validation fails, correct the reported field and run again. Before applying the result, check reference scope, model assumptions and any missing evidence or placeholder values.

Input field	Meaning	Value type	Requirement
callerCriticalFlowRatios	Caller critical flow ratios	list of number	Required
totalLostTimeSeconds	Total lost time seconds	number	Required

Enter nonempty nonnegative critical flow ratios with sum strictly between zero and one, plus nonnegative total lost time in seconds. Compute C=(1.5L+5)/(1−sumRatios) and allocate C−L in proportion to each ratio. No signal constraints, saturation-flow derivation or operational approval is included.

cycleSeconds=(1.5L+5)/(1−Y); effectiveGreen_i=(cycle−L)×ratio_i/Y

Use the exact units, boundary rules, ordering and missing-evidence conventions above.

Output field	Meaning	Value type
websterModeledCycleSeconds	Webster Modeled Cycle Seconds; follow the units, sign, ordering and evidence convention stated above	number
effectiveGreenSecondsByCriticalStage	Effective Green Seconds By Critical Stage; follow the units, sign, ordering and evidence convention stated above	list of number

json

{
  "input": {
    "callerCriticalFlowRatios": [
      0.2,
      0.3
    ],
    "totalLostTimeSeconds": 10
  },
  "output": {
    "websterModeledCycleSeconds": 40,
    "effectiveGreenSecondsByCriticalStage": [
      12,
      18
    ]
  }
}

Limitations and assumptions

Its arithmetic does not establish saturation flows or approve a signal plan. Interpretation depends on the units, sampling scope and exact model described above.

All listed fields require explicit values. Unexpected fields, incorrect types, nonfinite numbers and sparse evidence arrays fail validation; the specific bounds and alignment requirements are stated above. Extremely large inputs or outputs can also be rejected. An input error is distinct from a successful result reporting false, no matches or missing evidence.

Alternative or Complementary methods

Use Signal Progression Bandwidth Calculator for this related task: Signal progression compares green windows after shifting them to a shared travel-time basis.

Use Roundabout Capacity Calculator when its separate inputs and assumptions fit the question: A gap-acceptance roundabout model relates conflicting flow to critical and follow-up gaps.

References

Webster Signal Timing Calculator — tool.io

Similar or alternative tools

Signal Progression Bandwidth Calculator
Signal progression compares green windows after shifting them to a shared travel-time basis.
Roundabout Capacity Calculator
A gap-acceptance roundabout model relates conflicting flow to critical and follow-up gaps.