Curb Types Explained: Barrier, Mountable and Curb & Gutter

Why does a car tire stop dead against one curb but roll over another? The answer is the curb type. Highway agencies build curbs in a few basic shapes, and each shape does a different job.

What Are the Main Types of Concrete Curbs?

The main types of concrete curbs fall into three practical families: vertical (barrier) curbs, mountable or roll curbs, and curb and gutter. Caltrans puts it more formally, listing two general classifications, vertical and sloped. Curb and gutter then adds a flat drainage pan to a curb.

Caltrans says a curb is used mainly for channelization, access control, separation between pedestrians and vehicles, and delineation. It also notes that as operating speeds increase, lower curb height is desirable. Each agency names and sizes its own curbs, so every figure below stays tied to the agency that publishes it.

Need only the concrete for a run? The concrete curb calculator gives the volume, while this guide explains the types.

Barrier Curb: The Steep Vertical Curb

A barrier curb is the common name for a steep, near-vertical curb that deters vehicles from crossing. The highway manuals do not use the phrase “barrier curb”; Caltrans and TxDOT both call it a vertical curb.

Caltrans describes vertical curbs as nearly vertical, with an approximate batter of 1:4, and 4 to 8 inches tall. Its Type A curbs are 6 inches high, or 8 inches where local authorities request it and posted speeds are 35 miles per hour or less. TxDOT defines a vertical curb differently, as a face 6 inches or higher. WSDOT uses a 6-inch vertical curb to delineate the traveled way, to separate walkways from pedestrian refuges, and to grade-separate raised islands from the road.

One warning sits in all three manuals: a curb is not a traffic barrier. Caltrans states it plainly: “Curbs and dikes are not considered traffic barriers.” Where a vehicle must be redirected, a separate traffic barrier is used.

Curbs often run beside a sidewalk, so our guide on how wide a walkway should be covers that side of the layout.

Mountable and Roll Curbs for Driveways and Roundabouts

A mountable or roll curb has a low, sloped face that a vehicle can drive over. Caltrans calls these sloped curbs, with an approximate batter of 2:3 or flatter, 3 to 6 inches tall; its Type B faces use a 1:1.5 slope or flatter and are used for channelization, including raised median islands.

WSDOT draws the mountable line by face slope. A sloping face flatter than 1H:3V is mountable up to 6 inches, though WSDOT recommends 4 inches or less to avoid scraping a vehicle underside. WSDOT also uses mountable curbs in roundabouts.

TxDOT defines a mountable curb as a face less than 6 inches, and prefers 4 inches or less at some locations. These are three different conventions, so match a number to the agency that states it, and never blend them into one figure.

Curb and Gutter: A Curb That Also Drains

Curb and gutter is a curb cast together with a flat gutter pan, and its main job is drainage. Caltrans sums it up: “Curb with gutter pan serves the purpose of both curb and dike.” A dike is the element meant for drainage and erosion control.

The gutter pan carries water. Caltrans says gutter pans are typically 2 feet wide, in a range of 1 to 4 feet, with a cross slope of typically 8.33 percent to raise hydraulic capacity. Curbs with gutter pans, along with the shoulder, can form the roadway’s principal drainage system, with inlets set in the pan or the curb.

The curb part still follows the vertical or sloped rules above. Curb and gutter describes how the curb and pan are joined, not a new curb height.

How Much Concrete Does a Curb Run Need?

To size the concrete for a curb run, multiply the cross-section area by the length and add waste. The curb calculator does this, though it models the curb and gutter as plain rectangles, so it approximates the volume of a real battered or sloped face.

Take the calculator’s default: a 50-foot curb and gutter, with a 6-inch-wide by 18-inch-high curb and a 24-inch-wide by 6-inch-thick gutter pan, plus 10 percent waste.

1. Cross-section area. The curb is 6 x 18 = 108 square inches and the pan is 24 x 6 = 144 square inches, so the section is 252 square inches, or 252 / 144 = 1.75 square feet.
2. Volume for the run. Multiply by length: 1.75 x 50 = 87.5 cubic feet.
3. Add waste and convert. 87.5 x 1.10 = 96.25 cubic feet; divided by 27, that is 3.56 cubic yards.

These are the calculator’s rectangles, not an agency cross-section. Treat 3.56 cubic yards as an estimate for ordering, not a profile design, since a real barrier or mountable face has a batter that trims a little volume.

For other flatwork sizing, see how thick a slab should be and the structural concrete calculators.

Are Concrete Curbs Traffic Barriers?

No. All three manuals stress that a curb is not a traffic barrier. Caltrans notes that sloped curbs are mounted more easily than vertical ones, and that curbs are not generally adequate to keep a vehicle on the road.

The agencies also keep curbs away from fast traffic. TxDOT says curbs should not be used with high-speed through traffic lanes or ramp areas, and adds that curbs are used mainly on frontage roads, crossroads and low-speed streets. Caltrans advises avoiding curb where posted speeds are 40 miles per hour or more, except as noted in its tables.

Two Caltrans curbs sit outside the main three families:

• Median curb (Type D). 4 or 6 inches high, for raised traffic islands and medians where posted speeds are 45 miles per hour or more.
• Rolled gutter (Type E). A rolled gutter used only in special drainage situations.

FAQs About Concrete Curb Types

Sources and Further Reading

Pick the curb by its job: to deter, to be driven over, or to drain. Take the exact height and slope from your local agency’s Standard Plans. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated 2026-10-21.