TRAFFIC SPEED ESTIMATION PROCEDURE USED IN THE NIMPAC ROAD PLANNING MODEL

The traffic speed estimation procedure currently used in the NAASRA Road Planning Model (NIMPAC) is described. The procedure is almost identical to that developed by the Commonwealth Bureau of Roads in 1971-72. It is based on some Australian vehicle free speed data, interpretation of highway capacity manual methods and local practice, a limited search of the literature and a good deal of engineering judgement. Whilst appropriate for the purpose at that time the validity of many of the relationships should now be reviewed. The availability of an additional decade of research, more detailed road inventories and new "micro" traffic simulation programs such as TRARR means that improved general relationships can now be developed to incorporate in the "macro" road planning models of the 1980s. (TRRL)