There is no simple relation between traffic volume as a parameter determined locally and traffic concentration as an instantaneous parameter. The relations indicated by wardrop are valid only on the basis of a flow homogeneous in space and time and only for the expected values of the traffic parameters. It is not possible to determine numerically the random and systematic errors which can occur in the use of these relations. Nevertheless, they are frequently used in traffic engineering today. A consistent definition of the variables 'traffic volume' and traffic concentration' has been given by coers. The so-called space-time parameters defined there may be considered as the true parameters. However, their measurement in real traffic flow requires extraordinary efforts. Therefore, local or quasi-local measurements of traffic flow will continue to be important. The error due to local determination of traffic parameters must of course be recognized. Mathematical-statistical concepts of the relation between both groups of parameters have been elaborated to assess this error. These deductions have been supplemented by results of measurements on two-lane rural highways and of simulations. Results indicate that parameters determined locally constitute sufficient approximation to the corresponding space-time parameters. The errors due to these approximations can be calculated on the basis of the ideas outlined. Expecially for two-lane roads the differences between local parameters and space-time parameters have been quantified. (a) for the covering abstract of the symposium please see irrd abstract no. 224453.
Abstract