Calculate road crown elevation difference and cross-slope for drainage design. Supports normal (double) crown and one-way cross-slope configurations with AASHTO reference.
Grade lasers and dual-slope rotary lasers are the standard tools for verifying road crown in the field. Shop road grading equipment at Express Tools.
Shop Express Tools →Road crown elevation difference = (Road half-width ft) × (Crown % ÷ 100). A 24 ft road (12 ft each side) at 2% crown drops 0.24 ft (about 2.9 inches) from centerline to edge. Standard paved road crown is 1.5–2.0% per AASHTO; gravel roads use 3–4%.
Every road has crown — a deliberate transverse slope that sheds water to the gutters. A 2% crown on a 24-foot road drops the edge 0.24 feet (about 3 inches) below the centerline on each side. That seemingly small slope is enough to drain inches of rainfall off the pavement in seconds, protecting the subbase and providing safe wet-weather friction.
| Surface | Typical Crown | AASHTO Min |
|---|---|---|
| High-type pavement (asphalt, concrete) | 1.5–2.0% | 1.5% |
| Intermediate pavement | 2.0–3.0% | 2.0% |
| Low-type surface / stabilized | 3.0–4.0% | 2.5% |
| Gravel or crushed stone | 3.0–4.0% | 3.0% |
| Earthen road | 4.0–5.0% | 4.0% |
Road crown (or cross-slope) is the transverse slope built into a road surface to drain stormwater to the sides. Without crown, water ponds on the pavement — reducing friction, increasing hydroplaning risk, and accelerating pavement deterioration. A properly crowned road sheet-drains to the gutters within seconds of rainfall stopping.
AASHTO Green Book recommends 1.5–3.0% cross-slope for normal crowned roads. Paved surfaces use 2% as the standard crown. Gravel roads and shoulders need 3–4% due to higher surface roughness. Minimum is 1% to ensure drainage; maximum for normal crown is 4% (beyond that, superelevation design is needed for curves).
Double crown (normal crown) has the center of the road as the high point, with both lanes sloping toward their respective gutters. Single (one-way) cross-slope has the entire road width sloping in one direction — used on superelevated curves, parking lots that drain to one side, and roads with curbs on only one side.
Use a digital level or contractor's level across the road width. Read the cross-slope percentage. Alternatively, set a grade rod at the centerline and at the edge — the elevation difference divided by the half-width gives the crown slope. GPS with centimeter accuracy can also profile the cross-slope from a slow drive-by.
Yes. On curved sections, superelevation transitions from normal crown through a flat (0%) cross-slope to full superelevation. The crown removal transition and the superelevation runoff must both meet AASHTO minimum relative gradient requirements. Calculating the elevation difference across each lane is essential for setting paver screed and checking grade during construction.
Curb-to-curb or edge-to-edge
Typical: 1.5–3% for roads