Control site traffic speeds with practical checks. Reduce risk using clear taper and spacing targets. Keep crews protected while equipment moves, day and night.
Enter speeds, geometry, and vehicle assumptions.
| Scenario | Posted (km/h) | Target (km/h) | Zone (m) | Reaction (s) | Decel (m/s²) | Radius (m) |
|---|---|---|---|---|---|---|
| Urban utility work | 50 | 30 | 400 | 2.5 | 3.0 | 150 |
| Rural resurfacing | 80 | 50 | 700 | 2.5 | 3.2 | 250 |
| Bridge approach works | 60 | 40 | 500 | 2.0 | 3.0 | 180 |
Example values help demonstrate typical planning checks. Replace them with your project assumptions and approved traffic plan targets.
Speed conversion: v(m/s) = v(km/h) × 1000 / 3600
Reaction distance: dᵣ = v₁ × tᵣ
Braking distance for reduction: dᵦ = (v₁² − v₂²) / (2a)
Stopping distance at posted speed: dₛ = dᵣ + v₁² / (2a_f)
Friction-based deceleration: a_f = g × ((f + e) − slope)
Curve safe speed estimate: v = √(g × R × (f + e))
Travel time in zone: t = L / v₂
Following distance: d_f = v₂ × headway + vehicle_length
Where v₁ is posted speed, v₂ is target speed, tᵣ is reaction time, a is assumed deceleration, g is 9.81 m/s², f is friction, e is superelevation, R is curve radius, and slope is grade/100.
Construction corridors combine workers, heavy equipment, and unfamiliar road layouts. Speed reduction directly lowers crash energy and increases time to detect cones, flaggers, and lane shifts. Many sites target reductions of 10–30 km/h based on exposure and geometry. This calculator helps convert those targets into measurable distances and checks.
A typical perception–reaction time of 2.0–2.5 seconds can consume 28–56 meters at 50–80 km/h before braking begins. Braking distance depends on deceleration and available friction. On compacted surfaces, friction factors around 0.30–0.45 are common, while wet or dusty conditions may be lower. Use conservative values when uncertainty exists.
Speed-change tapers guide drivers into a reduced-speed environment and support consistent compliance. For example, an 80 to 50 km/h reduction often requires a longer transition than a 50 to 30 km/h reduction. If the recommended taper plus the reduction braking distance exceeds the available zone length, consider earlier warnings, a longer approach, or a lower target speed.
Horizontal curvature and grade can limit safe speed. The curve check uses radius with superelevation and friction to estimate a safe operating speed. Tight radii (for example, 120–180 meters) can require lower targets than straight segments, especially on wet pavement. Downhill grades effectively reduce available deceleration and can increase stopping distance.
Maintaining spacing reduces rear-end conflicts and allows vehicles to merge smoothly near lane drops. A 2.0 second headway at 30 km/h yields roughly 17 meters of time-based spacing, plus vehicle length. Use the following distance output to support queue control, pilot-vehicle operations, and safe access for haul trucks entering the work area.
1) What deceleration rate should I use?
Use 2.5–3.5 m/s² for comfortable reductions on public roads. For constrained sites, keep values conservative to reflect mixed vehicles and variable surfaces.
2) How should I choose the friction factor?
Start around 0.35 for typical paved conditions. Reduce it for rain, dust, loose aggregate, or temporary surfaces, and document the assumption in your traffic plan.
3) What does the stopping distance represent?
It combines reaction distance and braking distance from the posted speed. Use it to check whether warning placement and hazard clearance are adequate for expected drivers.
4) Why does curve radius affect the target speed?
Smaller radii increase lateral demand. The curve estimate checks whether your target speed stays within a friction and superelevation-based limit to help prevent loss of control.
5) What if the zone length check warns me?
If transition needs exceed available length, consider earlier signing, longer approach space, staged reductions, or a lower target speed so drivers can slow smoothly.
6) Can I use this for haul roads inside a project?
Yes. Enter site speeds and surface assumptions, then use outputs for spacing, stopping checks, and curve limits. For unpaved routes, use lower friction and conservative deceleration.
7) Are the results a substitute for regulations?
No. Treat results as planning estimates. Always follow approved traffic management plans, local requirements, and site safety procedures, especially for public interfaces.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.