Page 80 - SAPEM-Chapter-10-2nd-edition-2014

South African Pavement Engineering Manual
Chapter 10: Pavement Design

of deterioration that a pavement experiences. Consequently, in addition to the capital costs of road construction, the
total costs incurred by road agencies depend on the applied standards of maintenance and improvement.

The impacts of the road condition and design standards on road users are measured in terms of road user costs, and
other social and environmental effects. Road user costs comprise vehicle operating costs, costs of travel time and
the cost to the economy of road accidents.

Economic benefits from different road investment options are determined by comparing the total cost streams for
various road works and construction alternatives against a base case alternative. The base case is not doing the
project or doing the minimum, usually representing the minimum standard of routine maintenance. HDM-4
estimates the costs for a large number of alternatives year-by-year for a user-defined analysis period. All future
costs are discounted to the specified base year.

To make these comparisons, detailed specifications of investment programmes, design standards, and maintenance
alternatives are needed, together with unit costs, projected traffic volumes, and environmental conditions. Although
a substantial number of inputs to this system are required, only a few inputs and variables are project specific. The
rest remain unchanged for the larger economic environment. For this reason, road authorities requiring HDM
analysis usually adopt defaults, or standard inputs, for non-project related variables.

Section 5: Pavement Investigation and Design Process
Page 69