Motorists who leave their engines idling unnecessarily face an on-the-spot fine under plans being considered by councillors.

West Sussex County Council is seeking to reduce exhaust emissions by penalising drivers who refuse to turn off their engines while parked or waiting at railway crossings.

A pilot scheme expected to be introduced in January will allow traffic wardens to fine motorists who break the new rule.

A council spokesman said: “We want to get people out of the habit of leaving their cars ticking over out of convenience.”

Signs are already in place at level crossings ordering people to switch their engines off.

“We would stress that this is just an investigation at this stage,” the spokesman said. “If it was ever introduced the fixed penalty would probably be £20. But we would hope that the vast majority of motorists would be willing to cooperate.”

An Air Quality Management Area has already been set up in Shoreham, where the trial will take place. It will be expanded across the county if it proves successful.

Traffic wardens will be instructed to issue a warning to drivers who are caught with their engines idling. There will, however, be exemptions for lorries with freezer units and other vehicles that need to keep their engines ticking over.

Roger Turner, 30, a taxi driver from West Sussex, said: “Who gave them the right to tell us to switch off our engines? It’s not like we try to waste fuel.It’s just another example of the nanny state, telling us what we can and can’t do.”

Edmund King, president of the AA, said: “I think the council has to be careful. They need to run a high-profile campaign if they are going to do this because to prosecute people without telling them about it first would be very harsh.”