Calculator
Enter dimensions, choose units, then calculate the required widths.
Formula used
All widths are summed to estimate the overall section width.
| Carriageway | carriageway = total_lanes × lane_width |
|---|---|
| Paved width | paved = carriageway + median + shoulders(L+R) + bike(L+R) + parking(L+R) |
| Road platform | platform = paved + curb/gutter(L+R) |
| Right-of-way | ROW = platform + sidewalks(L+R) + buffers(L+R) |
| With allowance | ROW_with_allowance = ROW × (1 + allowance%/100) |
Auto lane-width suggestions are based on typical planning ranges and vary by speed and road type.
How to use this calculator
- Choose your length units and set the road type and environment.
- Enter design speed and total lanes for the roadway.
- Pick “Auto” lane width for a quick estimate, or enter a custom width.
- Add median, shoulders, and optional features like parking, bike lanes, and sidewalks.
- Include buffer/clear-zone widths if you are estimating right-of-way.
- Click “Calculate” to see results above the form, then export if needed.
Example data table
These examples are illustrative planning scenarios. Adjust to match your project and local requirements.
| Scenario | Lanes | Lane width (m) | Shoulders (m) | Median (m) | Sidewalks (m) | Buffers (m) | Estimated ROW (m) |
|---|---|---|---|---|---|---|---|
| Urban arterial with sidewalks | 4 | 3.50 | 0.50 + 0.50 | 0.00 | 2.00 + 2.00 | 1.00 + 1.00 | 20.00 |
| Rural collector with shoulders | 2 | 3.30 | 1.50 + 1.50 | 0.00 | 0.00 + 0.00 | 3.00 + 3.00 | 16.60 |
| Divided highway (basic median) | 6 | 3.60 | 2.50 + 3.00 | 4.00 | 0.00 + 0.00 | 5.00 + 5.00 | 45.10 |
| Urban street with parking | 2 | 3.20 | 0.00 + 0.00 | 0.00 | 1.80 + 1.80 | 0.60 + 0.60 | 14.80 |
| Complete street with bike lanes | 4 | 3.30 | 0.50 + 0.50 | 0.00 | 2.00 + 2.00 | 1.00 + 1.00 | 23.20 |
Road width planning notes
1) Why road width matters in construction
Road width drives earthworks limits, pavement quantities, drainage alignment, utilities corridors, and right-of-way coordination. A small change—such as adding a 2.0 m sidewalk on both sides—can add 4.0 m to the corridor, affecting boundary setbacks and service relocations. Early width estimates reduce redesign and help stakeholders agree on a realistic cross-section before detailed drawings begin.
2) Typical inputs engineers review
Functional class and design speed influence lane selection. Many projects use lane widths between 3.0 m and 3.65 m, depending on speed, vehicle mix, and context. Shoulders commonly range from 0.5 m in constrained urban streets to 2.5–3.0 m on higher-speed facilities. Median width varies widely: 0 m on undivided roads, about 1–6 m for basic separation, and more where landscaping or barriers are required.
3) What the calculator totals represent
This tool breaks the cross-section into carriageway, paved width, platform, and right-of-way. Carriageway is the lanes-only width. Paved width adds shoulders and optional lanes for parking or cycling. Platform adds curb/gutter where used. Right-of-way includes sidewalks and buffer/clear zones. Use the allowance percentage to apply a prudent margin for constructability, future widening, or survey tolerance.
4) Data checks to avoid rework
Confirm whether lane count is total across both directions, and ensure left/right features are entered per side. Verify that drainage space is not double-counted between curb/gutter and buffers. If the project includes a median barrier, check its footprint and shy distance. For urban streets, validate parking lane width and door-zone offsets when bike lanes are adjacent.
5) Using outputs in estimates and reviews
Exported results support quick quantity takeoffs and design reviews. Multiply width by segment length to estimate pavement area, then apply layer thickness for volume. Compare scenarios (for example, adding parking or bike lanes) to understand corridor impacts. Always align final values with local standards, safety audits, and site constraints before issuing construction documents.
FAQs
1) Is the lane width in this tool a code requirement?
No. Auto lane width is a planning suggestion based on speed and road type. Confirm the final lane width with your governing standards, design manual, and authority approvals.
2) What does “right-of-way” include here?
Right-of-way includes the platform plus sidewalks and buffer/clear zones on both sides. It does not automatically include extra space for utilities unless you enter it as buffer width.
3) Should I enter lanes per direction or total lanes?
Enter total lanes across both directions. For a 2+2 divided road, enter 4 lanes and include a median width if applicable.
4) How should I handle a raised median with barriers?
Select “Median included” and input the full median footprint, including barrier base if it occupies width. Add additional shy distance within buffers if your standard requires it.
5) Can I calculate in feet and still export correctly?
Yes. Choose feet, enter all widths in feet, and the results will display and export in feet. Internally, calculations convert to meters for consistency.
6) What is a good allowance percentage?
Use 0–5% for early concepts, and 5–10% when corridor constraints or future widening risks are high. The right choice depends on survey confidence and stakeholder requirements.
7) Does this include lane widening on curves or intersections?
Not automatically. If you need widening for curves, bus bays, turn lanes, or tapers, add those widths manually using parking/bike/buffer fields or adjust lane width in custom mode.