A QUIET 'rumble free' alternative to the rumble strips currently used to warn drivers of approaching hazards is being trialled in Hampshire.
The new corrugated surfacing produces noise and vibration inside the vehicle without increasing noise levels beside the road. It has been developed by roads research specialist TRL with funding from the then Department of Transport, Local Government & the Regions (DTLR).
Two trial sites were set up six months ago, in Farnborough and Fleet, and ambient noise measurements nearby are said to have seen no increase.
TRL found that the best results were obtained from a sinusoidal surface profile with a peak to trough amplitude of no more than 7mm and a wavelength of just 350mm.
'This worked with a wide range of road vehicles from small cars to HGVs, ' said TRL senior research fellow, professor Greg Watts.
'At road speeds of 30km/h to 65km/h, this profile produces a vibration frequency of 40hz to 50hz inside the vehicle, which is easily audible.'
Specialist contractor Prismo developed an ingenious laying technique to form the desired profile in a 15mm thick high performance, synthetic asphalt topping.
This involves a heavy steel roller running along profiled guide rails each side of the section being laid. The surface, dubbed 'Rippleprint', and the laying technique are being patented.