This paper was presented at session 34 - drivers, vehicles and geometrics 1. Rural free speed distribution data were examined for possible time trends in distribution parameters. It was found that, in Australia at least, the trend of increasing free speeds is continuing. The data also revealed a recent, parallel trend of decreasing speed coefficient of variation. Numerical investigations, based on simple queueing models, revealed that, in terms of queueing, these changes in speed distribution characteristics could be producing a 10-20 per cent improvement in two-lane rural road traffic operations. Current applications of the 'service volume' concept are examined in the context of this result. It is suggested that, while service volumes derived from the highway capacity manual are probably adequate for planning and design purposes, they should be seen as arbitrary values rather than measures of operating performance. As such, they are not appropriate for detailed considerations at the operational level. The number of the covering abstract of the conference is IRRD No. 239340.
Abstract