Dual carriageways are designed on the basis of commercial vehicles primarily occupying the slow lanes. Research has shown that only a proportion of total heavy traffic travels in the slow lane. The theory is that the flow in the second lane increases more rapidly as total heavy flow increases, and that a critical heavy flow level can be reached whereby flows in the inner and outer lanes are balanced. The paper addresses these factors utilising video surveys of dual carriageways and motorways. The variation in the rate of growth of heavy vehicle flow in each lane is measured against increasing overall heavy vehicle flow. An empirical relationship is derived from a database and presented both graphically and numerically. The reliability of the findings is tested statistically and compared with the observations of the Transport and Road Research Laboratory. This paper represents the early stages of a research programme which is continuing by investigating the influence of both geometric alignment and junction frequency on heavy vehicle lane occupancy behaviour on major roads. The work is relevant to the design and maintenance of dual carriageway and motorway pavements. Further, it should assist in the economic appraisal of crawler lane provision.
Samenvatting