Highway Engineering

Highway Pavement Materials and Design 205

Traffic flow at opening (cv/d) – 1 direction

100 1000 10000 30000

1

10

100

1000

Design traffic (msa)

75%

50%

25%

100%

OGV2

Figure 7.8Design traffic for flexible and flexible composite pavements (20-year design
life) – dual carriageway (HD 24/96) (DoT, 1996).

ing the cumulative design traffic over a 20-year design life for a flexible single
carriageway pavement. Figure 7.8 is a representation of the graph for flexible
dual carriageway pavements. Figure 7.9 represents the graph for a single car-
riageway rigid pavement (40-year design life). Figure 7.10 is a representation of
the graph for rigid dual carriageway pavements.
The million standard axle valuation derived from these graphs includes
an adjustment required to estimate the left-hand lane traffic which is
subsequently used for pavement design in Chapter 8 using HD 26/01 (DoT,
2001).
While economic studies have shown that a design life of 40 years is optimal,
flexible or partially flexible pavements are normally designed initially for 20
years, after which major maintenance is carried out.