Stopping Sight Distance Calculator

Stopping Sight Distance Formula

Worked Example

A level road designed for 80 km/h with t = 2.5 s and f = 0.35:

1. v = 80/3.6 = 22.22222222 m/s
2. SSD = v t + v² / (2g(f ± n)) = 55.55555556 + 493.8271605 ÷ (2 × 9.81 × 0.35) = 127.4686414 m

Braking distance v²/2g(f ± n): 71.91308584 m · Intermediate sight distance 2 × SSD: 254.9372828 m

GATE tip

On a two-way single-lane road, IRC requires twice the SSD because both vehicles must stop.

More Transportation Engineering Calculators

• 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 →

• Traffic Flow Calculator

  q = k v, v = vf (1 − k/kj)

  qmax = vf kj / 4 at k = kj/2 and v = vf/2

  Example: A road with vf = 80 km/h and kj = 120 veh/km at a density of 40 veh/km: Flow q = 2133.33 veh/h.

  Open the traffic flow 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 →

• 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.