Traffic Flow Calculator

Traffic Flow Formula

Worked Example

A road with vf = 80 km/h and kj = 120 veh/km at a density of 40 veh/km:

1. v = vf (1 − k/kj) = 80 × (1 − 40/120) = 53.33333333 km/h
2. q = k v = 40 × 53.33333333 = 2133.333333 veh/h

Capacity qmax = vf kj / 4: 2400 veh/h · Density at capacity kj/2: 60 veh/km · Speed at capacity vf/2: 40 km/h · Time headway 3600/q: 1.6875 s · Space headway 1000/k: 25 m

GATE tip

Every flow below capacity occurs at two densities (uncongested and congested); GATE questions usually want the lower one.

More Transportation Engineering Calculators

• Stopping Sight Distance Calculator

  SSD = v t + v² / (2g(f ± n))

  v in m/s, t = 2.5 s, f = 0.35–0.40, n = gradient as a fraction

  Example: A level road designed for 80 km/h with t = 2.5 s and f = 0.35: Stopping sight distance SSD = 127.469 m.

  Open the stopping sight distance calculator →

• Webster Signal Design Calculator

  C₀ = (1.5L + 5) / (1 − Y)

  Y = Σ q/s over critical phases; green gᵢ = (C₀ − L) yᵢ/Y

  Example: A two-phase signal with critical flows of 500 and 600 PCU/h, saturation flow 1800 PCU/h and 12 s lost time: Optimum cycle length C₀ = 59.1429 s.

  Open the webster signal design calculator →

• Superelevation Calculator

  e + f = V² / (127R)

  IRC design: e = V²/(225R) ≤ e max (7 %), f ≤ 0.15

  Example: A 300 m curve designed for 80 km/h: Design superelevation e = 7 %.

  Open the superelevation calculator →

• Equivalent Axle Load Calculator

  N = 365 A [(1 + r)ⁿ − 1]/r × D × F

  damage factor = (W/80 kN)⁴; N in standard axles (÷10⁶ for msa)

  Example: A 100 kN single axle compared with the 80 kN standard axle: Equivalent standard axles = 2.44141.

  Open the equivalent axle load calculator →

Frequently asked questions

Sources

• The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.