Consider long-term costs when choosing pavement alternatives

By John Emery and Dave Hein
John Emery Geotechnical Engineers

Selecting the most appropriate alternative for a particular pavement requires consideration of a number of factors, including both initial costs and life-cycle costs. Although the use of premium materials such as concrete pavers may increase the initial capital cost of construction, the performance benefits over the lifespan of the pavement can result in significant savings over conventional pavement alternatives.

In addition to increased service life that results from the use of premium materials in pavement construction, the adoption of a systematic and timely maintenance and rehabilitation program will increase pavement performance.

Life-cycle cost analysis

The pavement that is the least expensive for the owner is not necessarily the pavement that costs the least to construct. Rather, it is the pavement that gives the best return for the amount spent on it while it is in service.

The process to determine the best pavement alternative should be based on an economic analysis of the construction, maintenance and/or rehabilitation requirements for each pavement alternative.

For example, the use of interlocking concrete pavers can reduce pavement cut and repair costs, because:

• Expensive equipment is not required for removal;

• Pavers can be reinstated after the repair;

• Traffic interruptions and delays are reduced;

• When removed, there is no damage to surrounding units;

• Pavers do not leave visible patches to detract from the aesthetics.

To evaluate essentially equivalent (from a structural view point) design alternatives using different materials, it is necessary to consider not only the initial cost of each material, but also the total cost accumulated over its service life. The alternative having lower initial cost may not be the least expensive once factors such as maintenance, rehabilitation, inflation and interest (the value of money invested today for future use) are taken into account. The most effective method of measuring the cost effectiveness of alternative designs is life-cycle cost analysis.

Present-worth analysis

The present-worth method has been adopted by most agencies using life-cycle cost analysis procedures. This method requires knowledge of the rate of inflation, the interest rate, and the discount rate to accurately predict the life-cycle costs of each alternative.

Considerations for life-cycle cost analysis: Inflation rate Interest rate Discount rate Initial costs -- All costs to construct the selected pavement structure (capital cost). Maintenance costs -- Costs for systemic routine maintenance activities that increase pavement service life. Rehabilitation -- Costs for major maintenance activities including removal, regrading base and relaying or replacing damaged pavers when the pavement condition (riding quality for instance) reaches a certain minimum level of service ability (which generally depends upon of the classification of road or highway). Residual value -- The unused benefit (remaining service life) of any maintenance or rehabilitation activity at the end of the analysis period. Salvage value -- Value of any of the components that may be reused at the end of the analysis period. This may be a significant value for concrete pavers, as the individual pavers may be reusable. User costs -- The main user costs are vehicle operating costs, travel time costs, traffic delay costs due to construction, accident costs and discomfort costs. These user costs are difficult to quantify and should be expressed in terms of extra user costs over those usually anticipated.

The rate of inflation (the relative increase in price levels of commodities such as construction prices), and the interest rate (the rate of return on investment) vary depending on the economic climate of the time. The discount rate is equal to the interest rate minus the inflation rate.

The present-worth method equates present and future expenditures for each alternative, and associated maintenance and rehabilitation costs over the life of the project. This concept, known as discounting, is used to permit comparison of alternatives that require expenditures over an extended period, and allows the designer to consider the dual effects of interest rates and inflation on project costs.

Analysis period

The life-cycle analysis period used for pavements is generally 20 to 30 years. This reflects the trend by some agencies toward long-lasting pavements and the consideration of extended life-cycle analysis periods. It is generally acknowledged that pavements designed for longer traffic, or by life-cycle analysis, have lower life-cycle costs. It also represents the time period that the design axle loads and traffic must be considered for design purposes.

Life of pavement types

The service life of each pavement alternative also must be taken into consideration for equivalent life-cycle cost comparisons. The timing or schedule of each major maintenance and rehabilitation activity for each pavement alternative must be taken into account, and the most appropriate service life must be selected for life-cycle cost analysis.

More for the money

Life-cycle cost analysis is the most effective method of measuring the cost-effectiveness of alternate pavement designs for initial or maintenance pavement projects.

Public officials should recognize the need for a comprehensive engineering analysis, which should include life-cycle cost analysis for urban or rural new construction or rehabilitation projects.

A little extra time spent addressing life-cycle cost analysis at the beginning of a project means less time and money spent throughout the life of the pavement.

For more information on design and specification issues related to interlocking concrete pavers, contact the Interlocking Concrete Pavement Institute (ICPI) at 1323 Shepard Drive, Suite D, Sterling, VA 20164, (800) 241-3652, fax: (703) 450-0482, e-mail: ICPI@mail.wdn.com.

Copyright © 1998 Seattle Daily Journal of Commerce.