Traffic flows, representative of those on long span bridges on commercial routes in Britain, have been mathematically simulated and statistically analysed to determine 'characteristic' (1 in 2400 chance of exceedance in a year) live load effects which can arise when traffic jams occur. Loaded lengths in the range 75 - 1600m on single lane and two- and three-lane carriageways have been considered. Loading models have been based on traffic flows and mixes recorded in 1980 at various sites and are intended to represent conditions on a heavily trafficked commercial route. Those for 1990 have been extrapolated by use of predictions by TRRL of the growth of motorway traffic for each class of vehicle. They include allowance for the recent introduction of 38T 5 axle articulated lorries under the Construction and Use Regulations.

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