Roundabouts

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Proper traffic control is essential for ensuring the safety of motorists and non-motorized vehicles on KCRC's road and bridge network. KCRC adopts a strategic approach to road improvement and safety project selection with its mantra, "The right fix, at the right time, at the right location." Emphasizing the growing evidence supporting the benefits of roundabouts, KCRC actively explores integrating roundabouts in feasible and effective areas.


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Proven Safety Countermeasure Tool:

The roundabout is recognized by the Federal Highway Administration as a Proven Safety Countermeasure Tool. Its design effectively reduces intersection crashes, calms traffic, and minimizes delays. With only eight conflict points compared to 32 at traditional four-way intersections, roundabouts simplify decision-making for motorists. Moreover, the curved approaches and entry-yield control enhance safety by reducing vehicle speed, leading to a significant decrease in crashes causing injury or fatality.

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Studies by the Insurance Institute for Highway Safety show that roundabouts can provide a:

  • 90 percent reduction in fatal crashes
  • 75 percent reduction in injury crashes
  • 30 to 40 percent reduction in pedestrian crashes
  • 10 percent reduction in bicycle crashes

KCRC has been studying the effectiveness of roundabouts in other counties and investigating locations within Kent County that could accommodate and benefit from a roundabout. During the planning stage, many considerations are taken into account to determine the suitability of a roundabout for a particular location. KCRC engineers review safety and operational impacts,  available ROW, existing utility infrastructure, access management, operations of adjacent intersections, and the capacity to accommodate future traffic growth.

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Cost-Benefit Analysis

KCRC strives for cost-effective solutions with maximum benefits. For any type of intersection, a number of factors influence the economic investment. Costs associated with roundabouts include construction costs, engineering and design fees, land acquisition, and maintenance costs. Benefits typically include reduced crash rates and severity, reduced delay, fuel consumption, and emissions. 

Cost Comparison: Roundabout Versus Traffic Signal

The costs of installing roundabouts have been shown to vary significantly from site to site. A roundabout may cost more or less than a traffic signal, depending on the amount of new pavement area and the extent of other roadway work required.

At an existing unsignalized intersection, traffic signal installation can require roadway widening to provide the necessary lane configurations, including left turn lanes. In other cases, a traffic signal can be installed without significant modifications to the pavement area or curbs. Because the roundabout can rarely be constructed without significant pavement and curb modifications, these relative costs are evaluated.

While operating and maintenance costs of roundabouts are somewhat higher than for other unsignalized intersections, they are less than those for signalized intersections. In addition, traffic signals consume electricity and require periodic service (e.g., bulb replacement, detector replacement, and periodic signal retiming). Operating costs for a roundabout are generally limited to the cost of illumination.

While roundabouts may require more up-front capital investment to construct, their ability to reduce fatalities and injuries equates to cost savings for road users. AAA estimates that a single fatal motor vehicle crash costs the nation $6 million, considering lost earnings, lost household production, property damage, medical costs, and other factors. KCRC has leveraged and will continue to pursue Michigan Department of Transportation (MDOT) safety funding to offset construction costs. 

Lower Vehicle Pollution

Roundabouts mitigate stop-and-go traffic associated with traditional intersections, thereby reducing vehicle idling and pollution. By eliminating unnecessary stops and promoting continuous traffic flow, roundabouts contribute to lower levels of vehicle emissions.

Additional Considerations

KCRC carefully weighs the suitability of roundabouts for specific locations. Single-lane roundabouts may have limited capacity for higher traffic volumes, while multi-lane roundabouts present design and operational challenges. Factors such as unbalanced traffic flows, pedestrian volume, space constraints, variable traffic patterns, and the number of left-turning vehicles are carefully considered before considering a roundabout. Driver education is also an important component of installing a new roundabout.

Additional information can be found on the FHWA and MDOT websites.