Curve Widening Calculator

Inputs

Design Vehicle

Curve Radius (m)

Number of Lanes

Existing Lane Width (m)

Estimation only. Always consult applicable road design standards (TAC, AASHTO) and a licensed engineer. Terms

Result

—

m total widening required

Widening per lane—

Total road width (curved)—

Standard (straight)—

Curve classification—

What is this calculator for?

Roads need to be wider on curves because vehicles track differently when turning — the rear wheels follow a tighter path than the front. This calculator estimates how much additional width is needed based on the curve radius, number of lanes, and design vehicle. It follows principles from the TAC Geometric Design Guide.

How to use it

Select the design vehicle — use the largest vehicle that regularly uses the road
Enter the curve radius in metres — from your design drawings or survey
Select the number of lanes and existing lane width
Result is the total additional width required across all lanes on the curve

General guidance

R > 200m: Minimal widening needed

R = 100–200m: Moderate widening

R = 50–100m: Significant widening

R < 50m: Review design carefully

Standard lane width: 3.5–3.7m

Always verify: TAC / local standards