The Transport Research Laboratory (TRL) also undertook controlled tests in measured comparative trials, which delivered a steady state fuel savings of 3.8 per cent at a constant 52mph and 3.65 per cent at 40mph.
The tests took place at Millbrook's high-speed circuit in Bedfordshire, using a Volvo FM 6x2 tractor unit with a Cartwright tri-axle curtainsider trailer, which is widely used across the industry. Each test involved forty miles of high-speed circuit with cruise control set to maintain relevant test speeds. The two speeds chosen for the tests were 40mph, to replicate typical A roads, and 52mph, to mirror a typical motorway journey. Weather conditions throughout the test period remained constant.
During TRL's original wet weather trials engineers noticed a significant change in the behaviour of the spray plume around the rear of the vehicle. Subsequent Computational Flow Dynamics (CFD) modelled by scientists at Strathclyde University predicted that aerodynamics associated with the Spraydown flap design cause a reduction in drag, leading to worthwhile reductions in fuel consumption.