A speed hump is 12 to 14 feet long in the direction of travel and 3 to 4 inches tall at the apex, per the Institute of Transportation Engineers (ITE) Traffic Calming Manual Chapter 3 standard. The cross-section profile is most commonly parabolic (Watts profile), with sinusoidal and flat-top variants for cyclist-friendly and transit-compatible applications. The hump width across the road matches the lane width (8 to 14 feet typical) and extends curb-to-curb on most residential streets.
Standard speed hump dimensions
| Dimension | Standard Value | Range |
|---|---|---|
| Length (direction of travel) | 12 ft | 12 to 14 ft |
| Height at apex | 3.5 in | 3 to 4 in |
| Width across road | matches lane width | 8 to 14 ft |
| Profile shape | Parabolic (Watts) | Parabolic, sinusoidal, flat-top |
| Leading edge taper | 1 ft | 1 to 1.5 ft |
| Trailing edge taper | 1 ft | 1 to 1.5 ft |
Why is the length 12 to 14 feet?
The length defines the device. ITE Traffic Calming Manual Chapter 3 distinguishes humps from bumps explicitly by length:
- Speed bump: 1 to 3 ft long. Slows traffic to 5 mph (parking lots).
- Speed hump: 12 to 14 ft long. Slows traffic to 15 to 20 mph (residential streets).
- Speed table: 22 ft long (typical). Slows traffic to 20 to 25 mph (bus routes, fire access).
The 12 to 14 foot length matches the average wheelbase of a passenger sedan (10 to 11 feet front to rear axle). When a car crosses a 12-foot hump at 15 to 20 mph, the front and rear axles articulate the suspension at slightly offset times, creating smooth slowing without the abrupt jolt that a shorter bump generates.
Why is the height 3 to 4 inches?
Below 3 inches, the slowing effect drops below the threshold that drivers respond to. Above 4 inches, the device risks vehicle undercarriage damage and creates emergency-vehicle delays beyond what the FHWA recommends. The 3 to 4 inch sweet spot was empirically derived from field studies referenced in the ITE Traffic Calming Manual.
The 3.5-inch standard is the most common in practice. Some Oregon city traffic-calming programs spec 3 inches for streets with significant transit; some spec 4 inches for streets where 85th-percentile speeds run above 30 mph in pre-install surveys.
Watts (parabolic) profile dimensions
The Watts profile is a parabolic curve that rises from grade at the leading edge to 3.5 inches at the centerline, then descends back to grade at the trailing edge. Ordinate values at 1-foot intervals across a 12-foot Watts profile:
| Distance from leading edge | Height above grade |
|---|---|
| 0 ft (leading edge) | 0 in |
| 1 ft | 0.6 in |
| 2 ft | 1.1 in |
| 3 ft | 1.7 in |
| 4 ft | 2.3 in |
| 5 ft | 2.8 in |
| 6 ft (centerline) | 3.5 in |
| 7 ft | 2.8 in |
| 8 ft | 2.3 in |
| 9 ft | 1.7 in |
| 10 ft | 1.1 in |
| 11 ft | 0.6 in |
| 12 ft (trailing edge) | 0 in |
Sinusoidal profile dimensions
The sinusoidal profile uses a sine-curve cross-section across 14 feet. The 14-foot length and the smooth sine geometry deliver gentler slope at both ends, improving cyclist comfort. Ordinate values across a 14-foot sinusoidal profile:
| Distance from leading edge | Height above grade |
|---|---|
| 0 ft (leading edge) | 0 in |
| 1 ft | 0.2 in |
| 2 ft | 0.7 in |
| 3 ft | 1.4 in |
| 4 ft | 2.2 in |
| 5 ft | 2.9 in |
| 6 ft | 3.3 in |
| 7 ft (centerline) | 3.5 in |
| 8 ft | 3.3 in |
| 9 ft | 2.9 in |
| 10 ft | 2.2 in |
| 11 ft | 1.4 in |
| 12 ft | 0.7 in |
| 13 ft | 0.2 in |
| 14 ft (trailing edge) | 0 in |
Flat-top (speed table) dimensions
The 22-foot flat-top profile (technically a speed table, not a hump) consists of a 6-foot ramp up, 10 feet of flat top at 3.5 inches, and a 6-foot ramp down. Cross-section schematic:
| Section | Length | Height |
|---|---|---|
| Leading ramp | 6 ft | rises 0 to 3.5 in linearly |
| Flat top | 10 ft | constant 3.5 in |
| Trailing ramp | 6 ft | descends 3.5 to 0 in linearly |
Why is the width across the road usually full-lane?
Speed humps installed across only part of a lane create driver-weave behavior; cars steer around the hump, defeating the slowing purpose. Full-lane (curb-to-curb) coverage is the ITE standard. Speed cushions are the exception; cushions deliberately leave wheel-track gaps to let fire trucks pass through.
For multi-lane streets, the hump extends across all lanes. A two-way street with two 12-foot lanes uses 24 linear feet of hump material. A three-lane street uses 36 linear feet. Per-foot pricing scales with lane width; see speed hump cost per foot.
Frequently asked questions
What is the standard speed hump dimension? 12 ft long by 3.5 in tall, full-lane width across the road. The Watts parabolic profile is the U.S. residential default per ITE Traffic Calming Manual Chapter 3.
Why are speed humps 12 feet long? The 12-foot length matches passenger-car wheelbase. Cars cross at 15 to 20 mph with smooth suspension articulation. Shorter lengths jolt cars; longer lengths let cars maintain too much speed.
Is a 4-inch tall speed hump too tall? 4 inches is the upper end of the standard range. Some city programs spec 4 inches on streets with high pre-install speeds. Above 4 inches risks vehicle damage and is not recommended.
Can speed hump dimensions vary by jurisdiction? Slightly. Most Oregon city traffic-calming programs spec dimensions within the ITE 12 to 14 ft, 3 to 4 in range. Specific city standard details may pin specific values within that range.
What is the difference between a speed hump and a speed table dimension? Length. Humps are 12 to 14 ft; tables are 22 ft. Both are 3 to 4 in tall. The flat-top section on the table is the operational distinction that lets buses and fire trucks ride flat.
Specify Compliant Dimensions
Cojo installs speed humps across Oregon with ITE Traffic Calming Manual-compliant dimensions and city standard-detail matching. Contact Cojo for a site-specific spec, or see speed hump standards for full code reference.