Congestion on Britain’s roads is an increasing problem and in recent years traffic volumes have increased to such an extent that parts of the network are often operating close to capacity. The Department for Transport (DfT) and the Highways Agency (HA) are committed to reducing traffic congestion by better management of the road network. The movement of Abnormal Indivisible Loads (AILs) through the network causes additional delays which could be reduced by a better understanding of how delays are related to the type of load and the conditions under which they are moved, and of the comparative monetary and environmental costs of road transport and other modes, particularly water. This has been approached through literature review, consultation of stakeholders, monitoring of AILs both live and via detector data, and development of a spreadsheet based model which calculates the queues, delays and costs caused by an AIL movement along its entire route, depending on the day and time of travel. This model, verified using MIDAS data, exploits a novel analysis of extended queues caused by moving bottlenecks. The value of modelling has been confirmed by the highly variable nature of AIL congestion costs, and the model is being used to inform decisions about the route and timing of some AILs. The study confirms the sensitivity of congestion costs to the number of lanes occupied, which should be kept to the minimum consistent with safety. Better information about operational costs and environmental impacts would also be beneficial.

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