Previous research suggested that there could be worthwhile overall benefits from permitting a modest increase in the length of semi-trailers in the UK. The DfT decided that as part of its overall work on freight strategy, further research would be undertaken to consider in detail the feasibility and likely effects of longer semi-trailers, if permitted. The research was constrained to consideration of length increases up to a maximum of 2.05m and candidate vehicle configurations that would be capable of meeting all existing regulations (other than length). This would mean an increase in semi-trailer length from around 13.6m to no more than 15.65m, which would provide the same loading length as a rigid truck/drawbar trailer combination and represents the limit of what could be achieved under EU rules without the risk of having to accept longer combination vehicles. This would translate to an increase in overall length from 16.5m to around 18.55m. No increase in maximum permitted mass was to be considered.
The primary objective of the study was to establish whether the introduction of longer semi-trailers would be likely to deliver overall economic, environmental and societal benefits or dis-benefits.

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