A speed bump has been called a “sleeping policeman” (often in the plural “sleeping policemen") since at least 1968, when it was used in Jamaica. A “sleeping policeman” forces motorists to reduce speed.
The term “sleeping policeman” is now used throughout the world (especially in the Caribbean, Mexico and the United Kingdom), but is used in the United States mostly by immigrants.
Wiktionary: sleeping policeman
sleeping policeman (plural sleeping policemen)
1. (UK and Caribbean English, idiomatic) A speed bump.
(Oxford English Dictionary)
sleeping policeman n. a ramp in the road intended to jolt a moving motor vehicle, thereby encouraging motorists to reduce their speed.
1972 Daily Tel. 27 Oct. (Colour Suppl.) 23/3 (caption) ‘Sleeping policeman is a bump under the road surface designed to slow vehicles.
1974 Times 24 July 4/7 The government would proceed with experiments in the use of ‘sleeping policemen’—road humps to slow motorists.
“CAUTION . . . SLEEPING POLICEMAN” IS THE JAMAICAN WAY OF WARNING A MOTORIST TO BEWARE OF A RISE IN THE ROAD. “
Fourteen Islands in the Sun
By Charles Graves
New York, NY: Hart Pub. Co.
Unfortunately here and on other roads there are what the French call caniveaus, known locally as ‘sleeping policemen’, in other words, dry water troughs across the road which damage the springs of any motor car travelling at more than five miles an hour.
30 January 1968, The Daily Gleaner (Kingston, Jamaica), “Letters to the Editor: Sleeping policemen,” pg. 10, col. 4:
Many private roads in Kingston have installed “Sleeping Policemen”. It is more than problematic that, in an ever more complex world where the simple answer to a problem is no longer acceptable, these devices are being overlooked.
H. P. GARDINER (Col.)
(Highways and Bridges Committee, Worcestershire City Council.)
The Making of Cities
By Walter G. Bor
London, L. Hill
Above ‘Sleeping Policeman’ — corrugated strip across carriageway to slow down traffic in London Street, Norwich.
Traffic Planning and Engineering
By F. D. Hobbs
Oxford: Pergamon Press
The propriety of some control devices has been questioned and this includes the speed bump or so-called “sleeping policeman”.
Alternatives to the Private Car
By Terence Bendixson
Bloomington, IN: Indiana University Press
One way to warn drivers approaching semi-precincts would be to lay in the roads what one of my neighbour’s children calls ‘camel humps’ and what others have dubbed ‘sleeping policemen’.