TOWNS and cities throughout Britain are to spend millions of pounds replacing up to 500,000 road humps, because they are a potential hazard for new buses built with lower floors to allow wheelchair access.

The problem has arisen because of disability regulations introduced by the Government. Some buses will also have retractable ramps that will make their road clearance even lower. The regulations have already caused problems in some areas of London where the buses have been trialled and have run into trouble with the "sleeping policemen" humps.

London Transport has begun negotiations with councils to have the humps removed or reduced in height. Until this happens, roads with humps have been declared bus-less zones and routes now go along hump-free streets. Marsid Greenidge, the bus spokesman for London Transport, said: "Although low-floor buses can just about get over them, road humps can damage the undercarriage and provide an uncomfortable ride for passengers."

But because most side roads and suburban streets in the capital do have humps, London Transport said it will be impossible to re-route all buses and, even if it did, it would cause great inconvenience for passengers.Many bus services pass by schools and hospitals which are likely to be surrounded by road humps.

Since 1980 most councils have spent an enormous amount of money installing traffic-calming measures. The number of road humps in Britain may be as high as 500,000. The average cost of installing a hump ranges from £5,000 to £10,000. Replacing them could cost up £30 million.

Under the new regulations, by 2017 all buses will have to have low floors, so most new vehicles being bought by transport companies already comply with the regulations. Within five years it is estimated that half the buses on the roads will have low floors and be unable to cope with the humps.

This leaves councils with the prospect of ripping up all the humps laid and replacing them with lower ones or finding other traffic calming methods. A spokesman for Newham council in east London said that the cost of relaying all the borough's road humps would be prohibitive and re-routing buses would be the most cost-effective option.

However, the emergency services would be likely to welcome the lowering or scrapping of humps. Ambulances already have to go on special routes to avoid them when transferring critically ill people to hospital if there is a danger a sudden jolt could make their injuries worse.

The Department of Environment, Transport and the Regions has circulated advice to all councils warning them of the problems with new buses and asking them to take this into account when re-laying humps or planning new ones.

Paul Watters, the head of road and transport policy at the Automobile Association, said many councils had gone "over the top" and installed the largest possible humps in areas that didn't need them. He said: "Some humps are like climbing the Eiger. The maximum permitted height is 10cm and many councils have gone for this when 7.5cm is really all you need to slow traffic down. There is no doubt that these humps are preventing the new buses from serving the very areas they are most needed in."