Overtaking Distance Calculator

Work out overtaking distance instantly with clear inputs, formula shown and shareable results.

About Overtaking Distance Calculator

Overtaking time is the gap to close divided by the speed difference, and the clear road needed is your travel plus an oncoming vehicle's travel over that time. A 25 km/h speed advantage needs about eight seconds and over 400 m of clear road.

Formula

Overtaking sight distance

time = (vehicle lengths + safety gap) / relative speed; clear distance = (your speed + oncoming speed) x time

Worked example

With the default values below, Overtaking Distance Calculator returns Clear road needed of 426. Change any input above and every figure here is recalculated in your browser.

Inputs used

Your overtaking speed: 100 km/h
Vehicle being overtaken: 75 km/h
Combined vehicle lengths: 16 m
Oncoming vehicle speed: 90 km/h

Results

Clear road needed: 426 m
Time to complete the overtake: 8.06 s
Distance you travel overtaking: 224 m
Distance an oncoming vehicle covers: 202 m

Step by step

1Values used
2Overtaking sight distance
3Clear road needed= 426 m
4Time to complete the overtake= 8.06 s
5Distance you travel overtaking= 224 m
6Distance an oncoming vehicle covers= 202 m

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is the clear distance so long?

Because you and any oncoming vehicle close at the sum of your speeds. At 100 and 90 km/h that is 190 km/h, or 53 m every second.

What if the speed difference is small?

The overtake takes proportionally longer and becomes very dangerous. Below about 15 km/h difference on a two-lane road it is rarely worth attempting.