Costs Associated with Roundabouts
Many factors influence the amount of economic investment justified for any type of intersection. 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. Benefit-cost analysis is discussed further in Chapter 3.
When comparing costs, it is often difficult to separate the actual intersection costs from an overall improvement project. Accordingly, the reported 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 some existing unsignalized intersections, 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.
However, at new sites, and at signalized intersections that require widening at one or more approaches to provide additional turn lanes, a roundabout can be a comparable or less expensive alternative. While roundabouts typically require more pavement area at the intersection, they may require less pavement width on the upstream approaches and downstream exits if multiple turn lanes associated with a signalized intersection can be avoided. The cost savings of reduced approach roadway widths is particularly advantageous at interchange ramp terminals and other intersections adjacent to grade separations where wider roads may result in larger bridge structures. In most cases, except potentially for a mini-roundabout, a roundabout is more expensive to construct than the two-way or all-way stop-controlled intersection alternatives.
Recent roundabout projects in the United States have shown a wide range in reported construction costs. Assuming “1998 U.S. Dollars” in the following examples, costs ranged from $10,000 for a retrofit application of an existing traffic circle to $500,000 for a new roundabout at the junction of two State highways. National Cooperative Highway Research Program (NCHRP) Synthesis 264 (3) reports that the average construction cost of 14 U.S. roundabouts, none being part of an interchange, was approximately $250,000. This amount includes all construction elements, but does not include land acquisition.
Higher costs are typically incurred when a substantial amount of realignment, grading, or drainage work is required. The cost of maintaining traffic during construction tends to be relatively high for retrofitting roundabouts. This expense is due mainly to the measures required to maintain existing traffic flow through the intersection while rebuilding it in stages. Other factors contributing to high roundabout costs are large amounts of landscaping in the central and splitter islands, extensive signing and lighting, and the provision of curbs on all outside pavement edges.
Operating and maintenance costs of roundabouts are somewhat higher than for other unsignalized intersections, but 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 (similar to signalized alternatives, but typically more than is required for other unsignalized intersections).
Maintenance includes regular restriping and repaving as necessary, as well as snow removal and storage in cold climates (these costs are also incurred by conventional intersections). Landscaping may require regular maintenance as well, including such things as pruning, mowing, and irrigation system maintenance. To the extent that roundabouts reduce crashes compared with conventional intersections, they will reduce the number and severity of incidents that disrupt traffic flow and that may require emergency service.