New Project: Speed Impacts from Roundabouts and Other Traffic Control Devices

Roundabouts are effective at reducing driver speeds and lowering serious crash rates compared to other intersection types. Speeds vary in roundabouts, however, depending on geometric factors such as the number of lanes, entry and exit widths, and diameter. The use of supplementary control devices such as sign types, sign placement and pavement markings may also impact entry and exit speeds.

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Understanding how different roundabout elements impact driving speeds will inform improvements in geometric design and support speed setting and management efforts. Correlating design choices with safety implications will benefit road user safety and help address public concerns about roundabout intersections.

“The research will inform MnDOT and local agencies about speed control and design considerations of various roundabout features that impact driver speeds,” said Derek Leuer, state traffic safety engineer, MnDOT Office of Traffic Engineering. “While roundabouts currently exhibit excellent safety benefits, even greater safety improvements will bolster public support for this important intersection design.”

Objectives

In a new project, researchers will examine how roundabout geometries and traffic control devices impact driver speeds as they enter and exit roundabouts.

The objectives are:

Select roundabout study sites with varying geometric features, speed limits and land use contexts
Collect driver speeds upstream and downstream of roundabout intersections
Analyze vehicle trajectories to assess speed changes based on geometric and traffic control characteristics
Recommend design guidance for MnDOT and local agencies to estimate the impacts of roundabout features on driving speeds