Estimation of costs

Costs for a public works project are generally comprised of two elements: capitalized construction costs and operations and maintenance (O&M) costs. Although O&M costs are typically determined on an annualized basis, construction costs are typically a near-term activity that must be annualized. The following sections discuss these in more detail.

Construction costs

Construction costs for each alternative should be calculated using normal preliminary engineering cost estimating techniques. These costs should include the costs of any necessary earthwork, paving, bridges and retaining walls, signing and striping, illumination, and signalization.

To convert construction costs into an annualized value for use in the benefit-cost analysis, a capital recovery factor (CRF) should be used, shown in Equation 3-2. This converts a present value cost into an annualized cost over a period of n years using an assumed discount rate of i percent.

Operation and maintenance (O&M) costs

Operation and maintenance costs vary significantly between roundabouts and other forms of intersection control beyond the basic elements. Common elements include signing and pavement marking maintenance and power for illumination, if provided.

Roundabouts typically have a slightly higher illumination power and maintenance costs compared to signalized or sign-controlled intersections due to a larger number of illumination poles. Roundabouts have slightly higher signing and pavement marking maintenance costs due to a higher number of signs and pavement markings. Roundabouts also introduce additional cost associated with the maintenance of any landscaping in and around the roundabout.

Signalized intersections have considerable additional cost associated with power for the traffic signal and maintenance costs such as bulb replacement, detection maintenance, etc. Power costs vary considerably from region to region and over time and should be verified locally. For general purposes, an annual cost of $3,000 for providing power to a signalized intersection is a reasonable approximation.