A revolutionary road hump designed to deflate for emergency vehicles and drivers going under the speed limit has been unveiled.

The idea, which manufacturers claim is the world's first 'intelligent' road hump, was developed in Manchester to deflate for heavier vehicles such as ambulances and fire engines, or for cars travelling under a set speed limit.

Conventional 'sleeping policemen', made from concrete or asphalt, have drawn criticism for causing back and neck injuries, damaging suspension systems and increasing noise and pollution.

The new system, known as Transcalm, is made from rubber and contains a fast-working air valve that is triggered if a vehicle is over a certain weight or if it travels below a pre-programmed speed limit. This can be set between five and 40mph.

The system, developed by Dunlop GRG, highways consultancy Pell Frischmann and inventor Graham Heeks, has started trials in London.

Dunlop Transcalm chairman Mike Armstead said road humps were the most hated traffic calming scheme.

He said they caused injuries, had triggered boycotts from bus companies, slowed emergency services and had even sparked legal claims against local authorities.

Brian Simpson, of the Campaign Against Road-Hump Madness, said: "The design may be better for a single vehicle in isolation, but if other traffic is slow because of road humps then that slows emergency vehicles as well."