ROLE OF SHOULDERS IN TRAFFIC OPERATION

Highway shoulders are still the most neglected aspect of road design, construction, and maintenance, and tend to be poorly maintained. This literature on the operational effects of shoulder width is not very extensive. This paper presents a study of the effects of shoulder condition on traffic flow on four sections of main road in India. The shoulders studied were classified into good, average, bad, and worst. Data on traffic speed, traffic flow, and vehicle positions were recorded on each section. The average speed of single vehicles, and the average reduction in speed of a vehicle during a crossing or overtaking manoeuvre, were measured in situ; crossing operations were observed for cars and heavy vehicles only. Effective carriageway width is reduced if vehicles cannot use shoulders during passing and overtaking; this is more important on single and intermediate lane roads, where vehicles are often forced to get on and off the paved area. Data are given about the observed reductions in effective carriageway width and in speeds of cars and heavy vehicles, due to poor shoulder condition. The results are presented as tables. The authors recommend the development of a speed-flow relationship for roads with various shoulder qualities, to find out about the combined effect of width and speed reduction on capacity.