Section 4: Pavement Type Selection
Anchor: #i1009166Principal Factors
Selecting a pavement type is an important decision. Like other aspects of pavement design, the 1993 American Association of State Highway and Transportation Officials (AASHTO) Guide states, “The selection of pavement type is not an exact science but one in which the highway engineer must make a judgment on many varying factors. . ." Appendix B of the AASHTO Guide provides a list of principal and secondary factors to consider in the selection process.
Ultimately, the decision is at the district’s discretion; some principal factors for consideration may include:
- traffic (volume, percent heavy trucks, degree of congestion resulting from subsequent rehabilitation efforts)
- soils characteristics (shrink-swell potential, bearing capacity)
- climate/weather (amount of rainfall, icing potential)
- construction considerations (staged, urgency of quick completion, detour requirements, anticipated future widening)
- recycling (using material from existing structure or other sources)
- cost comparison (life-cycle cost analysis [LCCA] is preferred, but initial costs may dictate).
Secondary factors may include:
- performance of similar pavements in the area (similar structures with similar traffic history)
- adjacent existing pavement sections (continuity of cross section)
- conservation of materials and energy
- availability of local materials or contractor capabilities
- traffic safety (reflectivity properties under highway lighting, surface drainage, maintenance of skid properties)
- traffic noise mitigation (added)
- incorporation of experimental features (unique to one pavement type)
- stimulation of competition between major paving industries
- local preference.
Life-cycle Cost Analysis (LCCA)
LCCA is an engineering economic analysis tool that allows engineers to quantify the differential costs of alternative investment options for a given project. LCCA can be used to compare alternate pavement types (flexible versus rigid) on new construction projects and rehabilitation projects. LCCA considers all agency expenditures and user costs throughout the life of the facility, not just the initial investment, and allows for cost comparison of options with varying design lives to be compared on an equivalent basis.
More than a simple cost comparison, LCCA offers methods to determine and demonstrate the economic merits of the selected alternative in an analytical and fact-based manner. LCCA helps engineers answer questions like:
- Which design alternative results in the lowest total cost to the agency over the life of the project?
- To what level of detail have the alternatives been investigated?
- What are the user-cost impacts of alternative strategies?
LCCA’s structured methodology provides the information and documentation necessary for successful open dialogue. Because of this, LCCA is a valuable tool to support pavement type selection decisions.
The Federal Highway Administration (FHWA) has developed general guidance for running a detailed life-cycle cost analysis. This website is a good starting point for information on running a life-cycle cost comparison of alternatives.
TxDOT research project 0-1734 (Center for Transportation Research [CTR]) developed a computer program, TxPTS (Texas Pavement Type Selection). More information may be found at TxDOT Online Training. The program evaluates candidate flexible and rigid pavement strategies for pavement rehabilitation, reconstruction and new construction projects. The economic evaluations are based on life cycle cost analysis. Also, CTR developed a life-cycle cost analysis program for rigid pavements under project 0-1739.
LCCA is one tool for selecting a pavement type. The reliability of output from any LCCA is a function of the reliability of the input data. It may be beneficial to evaluate user costs separately from agency costs when looking at different structural options.