Montana Department of Transportation

Roundabouts

Purpose & Design

Why roundabouts?

A well-designed, strategically placed roundabout has several benefits:

Safety
Slower speeds and less conflict points reduces the frequency and severity of accidents.
Operation
Delays are reduced due to the smooth flow of vehicle traffic rather than the stop-and-go traffic of normal intersections.
Aesthetics
The central island is often landscaped to help beautify the intersection.

Design

There are no traffic signals or stop signs in a roundabout. To keep traffic flowing, most roundabouts have the following design feafures:

Yield at Entry
Traffic entering the roundabout yields the right-of-way to vehicles already in the roundabout.
One-Way Travel
Vehicles in a roundabout travel in one direction only (counterclockwise).
Central Island
A raised, painted, or landscaped central island.
Slower Speeds
Geometric features physically limit vehicle speeds to 25 mph or less.