This paper is concerned with efficient estimation of queues caused by moving bottlenecks or obstructions along whole routes of varied length and composition, under various operational and demand conditions, particularly where queuing spills back over several road sections. Arising originally from a need to predict the impact of unusual vehicles, the practical requirement is to build and calibrate a route model section by section, using simple and readily available descriptions and typical traffic patterns, without needing information about the surrounding network, and without iterative calculations. The approach necessarily involves some idealisation and approximation, so internal consistency and robustness are important considerations, as well as accuracy in the most common situations. Estimation of passing capacities (references given), and details like acceleration, deceleration, lane differences, merging, and stop-start 'shock waves' are not considered explicitly. Mathematical analysis with diagrams and examples is given. The underlying model relies on relationships between traffic flow, speed and density. These satisfy the so-called 'fundamental relationship',but a specific relationship between two of the variables is also needed. A speed/flow model is adopted for 'coupled' (non-free-flowing) traffic based on minimum distance and time headways, and calibrated to section speed and capacity characteristics. This form of model simplifies the description because it predicts that all discharge waves, and flow-change waves within queues, propagate upstream at the same speed (about 20 km/h). Queues are assumed to discharge at full carriageway capacity. There is some evidence that they discharge at a lower rate, but this could be addressed by separate research without affecting the basis of the model. The interface between section queues can take different forms depending on whether a gap of free-flowing traffic exists between them. The model automatically ensures the consistency of traffic flows and queuing conditions around the intersection. Practical implementation of the route model embraces several additional mechanisms, including delay to vehicles while passing the obstruction, holding up of opposite direction traffic particularly on single-carriageway sections, modification of traffic volumes by diversion, and breaks in journey allowing queues to pass. These are relatively straightforward to calculate by simple vertical queue modelling or modification of section variables. The core queue model could potentially be extended to networks by including random queue modelling to allow equilibrium queues at junctions to be represented. The sensitivity of results to the level of demand and turning proportions, and the effect of changes in road geometry, are illustrated by diagrams and calculated examples. Results are given for the wholeroute of a moving obstruction using motorway and other roads, showing that impact can be highly variable. Due to variations in ambient demand, the effect of journeys on different days and at different times is also highlyvariable, and not predictable by simple rules. Field measurements show there is no 'typical' result, confirming the need for disaggregate time-dependent modelling of individual cases. For the covering abstract see ITRD E135582.
Samenvatting