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A study was carried out to investigate, experimentally using a wind tunnel, the drag contribution (base drag) due to the flat-end of most van-type semi-trailers used for inter-city tractor-semi-trailer transportation. The study was focused on high cruise-speed operation of such vehicles at about 100 km/h (62.2 mile/h) a speed that can often be maintained for long distances on inter-city runs. It was found that it is possible to reduce overall aerodynamic drags significantly using a modestly tapered after-body terminating in a flat base. It was also shown that such after-bodies can be arranged to permit easy aft-end loading or unloading of trailers and that a reduction of engine fuel consumption at high-speed cruise on a level road of about 14% should be achievable when due allowance is also made for vehicle rolling resistance.