HC Deb 13 December 1983 vol 50 c387W
Mr. Rowe

asked the Secretary of State for Transport to what speed the humps of the design authorised by the Transport and Road Research Laboratory are intend to reduce (a) motor cycles, (b) motor cars, (c) lorries.

Mrs. Chalker

Road humps are designed for use on 30 mph roads. Experience has shown that the speed of vehicles on humps varies between about 10 and 18 mph, heavier vehicles, generally, being the slowest. Between humps speeds vary from about 20 to 30 mph, depending on the type of vehicle, the character of the road and the layout of the humps.