Safety Countermeasure Tool

Proper traffic control is integral to the safety of motorists and non-motorized vehicles using KCRC’s road and bridge network. The strategy that we apply to road improvement selection, "The right fix, at the right time, at the right location," also applies to safety project selection. With growing evidence supporting the benefits of roundabouts, KCRC continues to consider this intersection design and seeks to integrate roundabouts at locations where a roundabout would be feasible and effective.

The roundabout is identified by the Federal Highway Administration as a Proven Safety Countermeasure Tool because of the design’s ability to reduce intersection crashes, calm traffic and reduce delay. The design’s counterclockwise flow around a central island simplifies motorist decision making and minimizes conflict points. At a four-way intersection, there are 32 possible conflict points between vehicles. Alternatively, there are only eight conflict points between vehicles within a roundabout. The curved approaches reduce vehicle speed, and the entry-yield control keeps circulating traffic flowing. Data has found that the lower speeds and reduced conflicts can substantially reduce crashes that cause injury or fatality.

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

For these reasons, 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 must be taken into account to determine the applicability of a roundabout, including ROW, utilities, access management, operations of adjacent intersections, safety impacts, existing and predicted future traffic volume, and driver education.

Cost-Benefit Analysis

KCRC seeks to utilize funding in a manner that produces the greatest benefit for the least cost. For any type of intersection, a number of factors influence the economic investment justified. Costs associated with roundabouts include construction costs, engineering and design fees, land acquisition, and maintenance costs. Benefits may include reduced crash rates and severity, reduced delay, stops, fuel consumption, and emissions. 

Cost Comparison: Roundabout Versus Traffic Signal

At an existing unsignalized intersection, typically a traffic signal can be installed without significant modifications to the pavement area or curbs. In these instances, a roundabout is likely to be more costly to install than a traffic signal, as the roundabout can rarely be constructed without significant pavement and curb modifications.

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.

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.

While roundabouts may often be more expensive to construct, but 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, taking into account lost earnings, lost household production, property damage, medical costs, and other factors.

Lower Vehicle Pollution

Vehicles entering a roundabout must yield at entry but are not required to stop if the roundabout is clear. This eliminates some stop-and-go traffic associated with stop sign or traffic signal-controlled intersections. This leads to fewer vehicles idling while stopped at an intersection.

Roundabout Requirements

As stated, KCRC seeks to consider roundabouts at locations where a roundabout would be feasible and effective. The bullets below illustrate a roundabout’s limitations or instances for which a roundabout would not be ideal.

  • Single-lane roundabout may not provide enough traffic volume capacity
  • Multi-lane roundabout can be difficult in terms of design and operation
  • The delay and safety experience at a multi-lane roundabout is sensitive to small geometric characteristics
  • An intersection with highly unbalanced traffic flows (that is, a very high traffic volume on the main street and very light traffic on the side street) may not be an ideal candidate
  • A roundabout may not be appropriate where there is a high volume of pedestrians wishing to cross, as this may impact the capacity of the roundabout to process vehicles
  • The location under consideration lacks the room needed to build the roundabout
  • The location under consideration has significantly variable traffic patterns for which a traffic signal can better adapt
  • The location under consideration has a high number of left turning vehicles

First Roundabout: 84th Street and Kalamazoo Avenue

A traffic signal is needed at 84th Street and Kalamazoo Avenue. However, our research suggests that a roundabout could result in a safer intersection, and the location meets roundabout requirements. Therefore, KCRC applied for, and was awarded, Federal Highway Safety Improvement Program (HSIP) grant.

Ultimately, KCRC’s decision to apply for a grant at 84th Street and Kalamazoo Avenue was based on the following factors:

  • The intersection meets the traffic volume requirements for the installation of a traffic signal 
  • The intersection experiences peak-hour delays
  • There are vision corners on both the northwest and southwest corners which should provide adequate right of way to construct a roundabout. The capacity analysis shows that a single-lane roundabout would provide adequate capacity even with the anticipated traffic increase that would result should the proposed development be constructed (Because this would be the first of its kind in the county road network, the staff seeks to select a location that can benefit from a single-lane (rather than multi-lane) roundabout.)
  • Comparing a traffic signal to a roundabout using the HSM predictive method to calculate anticipated crash reduction shows that a roundabout would help produce 2.38 fewer crashes per year, 0.70 fewer injury crashes, and 1.68 fewer property damage crashes.  Based on National Safety Council crash costs, the project has a 4.75-year time rate of return.
  • No monthly costs related to signal energy or signal maintenance would equate to future savings

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