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Many of the speed, flow and density relationships postulated in different literatures are based on empirical evidences collected under favourable conditions. Those that veered into comparative analysis under contrasting conditions often use forced curves to describe the relationship between speed and flow mainly because the graph is not a function. However, the paper is an attempt to postulate that dynamic speed-flow, speed-density and flow-density functions have similar behavioural pattern. In the study, speed and flow relationship under adverse road surface condition depicted with potholes and edge subsidence among others was investigated. The study was carried out in Nigeria where adverse road surface condition on principal roads is prevalent under daylight, dry weather and off-peak conditions. It is based on the hypothesis that adverse road surface condition has significant impact on otherwise uninterrupted traffic stream. The paper compared empirical survey data from 11 locations on roadway segments with control and adverse sections. Optimum speeds for control and adverse road sections were estimated and compared. The study found 50% reduction in optimum speed and concluded that significant speed reduction will occur under adverse road surface condition.
adverse-conditions, dynamic, speed-flow, speed-reduction
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