Road Width Requirement Calculator

Work out road width requirement instantly with clear inputs, formula shown and shareable results.

About Road Width Requirement Calculator

Access road width is driven by peak hour demand. Daily trips are the plot count times trip generation per plot, and the peak hour is typically ten to fifteen percent of the daily total. Dividing by lane capacity gives the number of lanes, at 3.5 metres each, with a two lane minimum for two-way access regardless of demand.

Formulas

Peak demand

Peak hour trips = plots x trips per plot per day x peak hour share

Width

Lanes = max(2, ceil(peak trips / lane capacity)); width = lanes x 3.5 m

Worked example

With the default values below, Road Width Requirement Calculator returns Carriageway width required of 7.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Plots servedminimum 1: 60
Vehicle trips per plot per dayminimum 0.1: 6
Peak hour share of daily tripsaccepts 1–40 %: 12 %
Lane capacityminimum 10 vehicles/h: 600 vehicles/h

Results

Carriageway width required: 7.00 m
Peak hour trips: 43 vehicles/h
Traffic lanes required: 2
Capacity provided: 1,200 vehicles/h

Step by step

1Values used
2Peak demand
3Width
4Carriageway width required= 7.00 m
5Peak hour trips= 43 vehicles/h
6Traffic lanes required= 2
7Capacity provided= 1,200 vehicles/h

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.
Preliminary estimate only. Road widths in a layout are set by development control regulations including fire access and utility corridor requirements.

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

Preliminary estimate only. Road widths in a layout are set by development control regulations including fire access and utility corridor requirements.

Frequently Asked Questions

How is the Road Width Requirement figure worked out?

Peak hour trips = plots x trips per plot per day x peak hour share. Access road width is driven by peak hour demand.

Is capacity the only consideration?

No. Minimum widths for fire tender access, on-street parking, footpaths and utility corridors usually govern on residential layouts long before traffic capacity does.

What values do I need to enter?

This calculator takes 4 inputs: Plots served, Vehicle trips per plot per day, Peak hour share of daily trips, Lane capacity. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.