The chart below shows how each factor changes the lane width recommendation.
| Scenario | Road type | Speed (km/h) | AADT/lane | Heavy vehicles (%) | Shoulder (m) | Curve radius (m) | Suggested lane width (m) |
|---|---|---|---|---|---|---|---|
| Urban corridor | Urban Arterial | 60 | 1800 | 8 | 1.2 | 500 | 3.45 |
| Rural freight route | Rural Arterial | 90 | 2200 | 22 | 2.0 | 900 | 3.95 |
| Town center street | Urban Local Street | 30 | 450 | 4 | 0.5 | 120 | 3.10 |
| Industrial access road | Industrial Access Road | 40 | 900 | 30 | 1.0 | 250 | 4.05 |
Lane width = base width + speed adjustment + traffic adjustment + vehicle adjustment + heavy vehicle adjustment + shoulder adjustment + curve adjustment + clearance adjustment + bicycle adjustment + parking adjustment + right of way adjustment
Rounded lane width = round(recommended lane width ÷ 0.05) × 0.05
Carriageway width = lane count × rounded design lane width
Total cross section width = carriageway width + 2 × shoulder width
Margin = rounded design lane width − design vehicle width
The base width depends on the road class. Adjustments then widen or tighten the lane according to speed, traffic volume, truck share, shoulder support, curve sharpness, roadside clearance, bicycle activity, curbside parking, and corridor constraints.
- Choose the road type that best matches the project corridor.
- Enter lane count, design speed, and AADT per lane.
- Set the design vehicle width and truck percentage.
- Provide shoulder width, curve radius, and side clearance.
- Select bicycle activity, parking condition, and right of way constraint.
- Press Calculate Lane Width to see the result above the form.
- Review the adjustment table, fit rating, graph, and engineering notes.
- Use the CSV or PDF buttons to save the report.
1) What does this calculator estimate?
It estimates a practical lane width for preliminary roadway design. The result combines a base lane width with adjustments for traffic, speed, heavy vehicles, side conditions, and corridor constraints.
2) Is the result a final code compliant design?
No. It is a screening tool for planning and comparison. Final dimensions should always be checked against the design code, agency policy, safety review, and project specific drawings.
3) Why does truck percentage increase lane width?
Heavy vehicles need more operating space and usually create greater side friction. As truck share rises, a wider lane often improves comfort, clearance, and stability, especially on freight routes.
4) How does curve radius affect the answer?
Sharper horizontal curves can require more width because vehicles off-track and drivers need added comfort. A smaller curve radius therefore increases the widening adjustment in this calculator.
5) Why is curbside parking considered?
Parking adds door opening risk, vehicle movement, and lateral friction near the lane edge. The calculator applies a widening allowance when parking is present beside the travel lane.
6) What is the lateral operating margin?
It is the difference between the selected lane width and the design vehicle width. Larger margins usually improve comfort and recovery space, while small margins signal tighter operating conditions.
7) Can I use this for urban and rural roads?
Yes. The calculator includes several road classes and lets you adjust the operating environment. It suits early comparisons for local streets, arterials, collectors, freeways, and industrial roads.
8) What should I do after getting the result?
Review the notes, compare the minimum and future ready widths, and check the cross section impact. Then verify the chosen lane width with local standards, drawings, and safety requirements.