Vibration free 'sleeping policemen' are under development in Holland in a bid to cut down the associated noise and potential damage to adjacent buildings. A recently completed £15,000 trial carried out in a factory compound featured a typical road hump mounted on 36 neoprene-damped antivibration mounts. The hump was also surrounded by a flexible noise-reducing perimeter skirt. Variables measured during the trials included vehicle speed and weight, humidity and temperature and forces on the mounts. A 5dB reduction in associated noise was achieved.
Road trials featuring a stiffer damping material are to start soon, funded by the same consortium of a local acoustical consultant, a damping material manufacturer and a major road contractor. The Dutch government is said to be watching the trials with interest.