This paper describes a research project, which presents the results of analysing speed-flow relationships at about 100 sites throughout the UK. The speed bands used were 0-15 mph, then 12 other bands at 5 mph intervals up to 65 mph. Data were collected during the period 07.00 - 19.00. Histogram plots of traffic flows in given speed bands were analysed statistically. The analysis was designed to answer the following questions: (1) Do urban sites exhibit a speed-flow curve, and what is the shape of any such curve? (2) Can these curves be classified? (3) What influences their classes? and (4) Is there any relation between classes and accidents? For the first time, investigations have shown that a wide range of urban roads can be classified according to their speed-flow characteristics. Five very distinct speed-flow classes were found, that seem to be well correlated with road type. The predicted best-fit lines for each class are generally very good. Traffic-calmed roads form a very distinct class, with speed distribution shifted downwards by about 10 mph. It seems likely that speed-flow classes can be allocated to urban road networks, for example as a basis for accident modelling and prediction work.
Abstract