Estimating vehicle kilometers of travel using PPS sampling method

The estimation of vehicle kilometers of travel at various levels of a road network is one of the key tasks of any road and transport authority. This paper introduces a method to estimate the vehicle kilometers of travel. Stratified probability proportional to size (PPS) cluster sampling has been applied as a developmental tool in the kingdom of Morocco. The PPS sampling is based on classical statistical theory. Using the PPS sampling together with stratified sampling, it is possible to optimally allocate counting resources so that an acceptable level of reliability can be obtained in different parts of the network. In addition, the costs of countings may be included as part of the optimization. The PPS method requires some historical data to weigh different clusters of the road network according to their importance. However, mechanical approaches based on statistical theory alone do not result in satisfactory solutions, but the counting system should also be evaluated taking into account technical, economical, and organizational factors.