Abnormal Indivisible Loads (AIL) range from vehicles slightly larger than HGVs to massive transporters specialised for heavy loads like electricity transformers. The HA is responsible for authorising the largest and heaviest movements under Special Order regulations. To help meet the DfT’s PSA network delay target, the HA needs to know their likely impact, and the possible benefit of managing routes and schedules. The report describes a project to extend the modelling already implemented in the ‘AIL Congestion Calculator’ spreadsheet program, and to apply it to estimating impact on the PSA value. Modelled delays of simulated AIL moves on specified routes are first translated into a profile of impacts on all the PSA measurement routes affected. Then a new program, the ‘PSA Value Calculator’, merges ‘modified days’ representing the AIL moves with reference charts of measured journey times on the PSA routes, and uses a standard procedure to calculate the impact on the network PSA value. The report also describes a modelling exercise leading to estimation of the generic PSA impact of a range of AIL types on primary route segments of different type and length, which can be used to estimate the impact of one or more AIL moves.

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