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South African Pavement Engineering Manual
Chapter 10: Pavement Design

• Category D roads. Low volume and experimental roads are often also classified as Category D roads. The
traffic growth on category D roads can be rapid and unpredictable. A short structural design period enables
changes in the initial life cycle strategy to adapt to changing circumstances, without any major financial
implications. A design reliability of 50 percent implies that half the pavement is distressed at the end of its design
period.

3.3 Life Cycle Strategies

The purpose of pavement design is to identify the most economic design, with sufficient structural capacity, for the
particular design situation. Various alternative designs are initially identified, considering the availability of materials,
structural capacity demand of the actual traffic spectrum, and the service level of the facility. The ultimate selection
of a particular design, however, depends on an economic analysis of the design options over the full life cycle of the
facility. The strategy for some of the design alternatives may call for more capital investment for the initial
construction to ensure a longer structural design period, while others may have a bigger demand for maintenance
funds.

The design strategy and economic analysis of the full life cycle of the facility require an understanding of the
behaviour of different pavement types, and the type and timing of maintenance and rehabilitation expected during
the life cycle. An understanding of material and pavement behaviour is therefore critically important.

Figure 6 illustrates three possible design strategies for the design of a new facility. Alternative strategies are
normally compared on the basis of the least Present Worth of Cost (PWOC). The successful realization of any design
strategy depends on the constructability, maintainability and salvage value of the design. See Section 5.4 for more
discussion on economic analyses.

Section 3: Design Considerations
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