How Tall Are Speed Bumps? Height & Dimensions Guide

Speed bumps measure 3 to 4 inches tall at centerline per the ITE Traffic Calming Manual, with 3.5 inches the most common spec across US parking-lot installs. Below 3 inches and the bump doesn't actually slow anyone. Above 4 inches and you start damaging low-clearance vehicles at parking-lot speeds. The FHWA Traffic Calming ePrimer lands on the same height window.

Below: why 3 to 4 inches is the engineered sweet spot, what goes wrong outside that window, and how the 75th-percentile rule ties bump height to target speed.

What Is the Standard Height of a Speed Bump?

Standard parking-lot speed bump height in 2026:

Bump Type	Standard Height (Centerline)
Light-duty residential	2.5 to 3 inches
Standard parking lot	3 to 4 inches
Heavy-duty commercial	3.5 to 4 inches
Speed hump (residential street)	3 to 4 inches (different length, same height)
Speed table (collector street)	3 to 4 inches (different length, same height)

Across all four major bump categories, height stays in the 3 to 4-inch window. Length is what changes — a 1-foot bump produces 5 mph parking-lot speeds, a 12-foot speed hump produces 15 to 20 mph street speeds. Both share the same height range.

Why Is 3 to 4 Inches the Engineered Sweet Spot?

Three engineering constraints anchor the height range:

• Vehicle clearance. Most passenger vehicles have ground clearance of 5 to 7 inches at the lowest point (oil pan, exhaust, suspension). A 3 to 4-inch bump with a parabolic profile clears safely at 5 mph.
• Driver discomfort threshold. SAE-cited engineering studies show passengers perceive vertical acceleration above roughly 0.5 g as uncomfortable. A 3-inch bump at 10 mph produces about 0.5 g; at 20 mph it produces more than 1 g, which forces drivers to slow.
• Suspension damage threshold. Heights above 4.5 inches at parking-lot speeds (5 to 15 mph) produce suspension contact and oil-pan contact on common passenger sedans. Insurance claims spike sharply.

The 3 to 4-inch window is the band where bumps are uncomfortable enough to slow drivers without damaging compliant vehicles.

What Happens If a Speed Bump Is Too Tall?

Bumps above 4 inches at parking-lot length produce three predictable failures:

• Vehicle damage at parking-lot speeds. Compliant drivers crossing at 5 mph experience suspension contact. Liability lawsuits follow.
• Avoidance behavior. Drivers swerve onto sidewalks, landscape strips, or the wrong side of the lane to avoid the bump. The traffic-calming benefit inverts.
• Emergency vehicle damage. Fire trucks, ambulances, and police cruisers crossing at 15 to 25 mph during emergencies suffer suspension and undercarriage damage. Local fire codes (Portland Fire Code, NFPA 1141) often prohibit non-compliant heights on fire-access routes.

ITE Traffic Calming Manual chapter 3 specifically warns against custom-height bumps. Insurance liability for non-standard heights runs significantly higher than for ITE-spec bumps.

What Happens If a Speed Bump Is Too Short?

Bumps below 3 inches produce a different failure mode:

• Drivers do not slow. A 2-inch bump at 25 mph produces sub-0.3 g acceleration — uncomfortable but tolerable. Drivers maintain speed.
• The bump becomes invisible. A 2-inch height blends with pavement settlement, especially under chevron paint that hides the profile.
• Traffic-calming effectiveness drops to near zero. ITE meta-analysis shows bumps below 3 inches reduce average speed by less than 5 percent.

Property managers sometimes spec sub-3-inch bumps to avoid complaints. The result is paying for a traffic-calming device that does not calm traffic.

How Does the 75th-Percentile Rule Apply?

The Institute of Transportation Engineers Traffic Calming Manual references the "85th percentile speed" rule from highway engineering for street speed humps and tables, and a related "75th percentile" rule for parking lots. The principle: the bump should be uncomfortable enough at the 75th-percentile observed speed that drivers slow to comply.

For a parking lot where 75 percent of drivers travel at or below 12 mph, a 3-inch x 1.5-foot bump produces enough vertical acceleration to slow that 75th-percentile driver. For a parking lot with chronic 20 mph traffic, a 4-inch x 1-foot bump or a paired bump-cushion arrangement may be needed.

ITE references the 75th-percentile observation as the design speed input. Skipping the speed survey produces undersized or oversized bumps.

Are Some Heights Required by Code?

Federal code (Manual on Uniform Traffic Control Devices, mutcd.fhwa.dot.gov) does not formally standardize speed bumps as roadway devices because they do not appear on public highways. State and local codes set their own specs:

• Oregon DOT references ITE Traffic Calming Manual specs for residential traffic-calming installs (oregon.gov/odot)
• Portland PBOT specifies 3.5-inch height for traffic-calming program speed humps (portland.gov/transportation)
• Salem PW Chapter 79 references 3 to 4 inches for residential speed humps
• Eugene EPP specifies 3 to 3.5 inches for neighborhood-greenway speed humps

Private commercial parking lots in Oregon are not bound by these specs but most contractors default to 3 to 4 inches for liability and ITE-compliance reasons.

For deeper code context, see speed bump standards MUTCD. For dimensional spec across all three measurements (height, length, width), see speed bump dimensions.

Does Height Affect Vehicle Damage Risk?

Yes, in concert with length and approach speed. Per Cojo field experience and ITE references:

• 3 inches at 5 mph: zero damage risk on compliant passenger vehicles
• 3 inches at 15 mph: mild suspension stress; no damage on most vehicles
• 4 inches at 10 mph: mild suspension stress
• 4 inches at 20 mph: suspension damage risk on low-clearance vehicles
• 5+ inches at any speed: damage risk on most passenger vehicles

For deeper damage-risk analysis, see do speed bumps damage cars.

On a 14,000-square-foot Salem retail center we restriped in March 2026, the owner inherited four speed bumps measuring 4.5 inches at centerline. Two years of vehicle-damage complaints — primarily oil-pan contact on low-clearance sedans — preceded our visit. We replaced all four with 3.5-inch ITE-spec bumps. Complaints stopped.

For Oregon paving-and-marking pricing context, see our asphalt paving cost Oregon breakdown. For Portland Metro commercial spec context, see Speed Bumps in Portland Metro.

Get a Site-Surveyed Quote

Speed bump height should match traffic load and target speed at your specific site. Get a custom quote and Cojo's estimator will conduct a 75th-percentile speed observation, recommend ITE-compliant height, and verify cross-section before install.

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