London drivers are getting confused by signs for the Low Emission Zone (LEZ), a motoring organisation has warned.
Only the most heavily polluting lorries face charges to enter London
The Automobile Association (AA) said it received hundreds of calls from baffled motorists who did not understand the purpose of the LEZ or who it affected.
Road users were particularly confused by the signs which have sprung up across London and out to the M25.
From Monday morning the most heavily polluting lorries faced charges of £200 per day to enter Greater London.
Cameras check all lorries over 12-tonnes entering the zone against a database of vehicles certified as meeting EU exhaust limits.
AA president Edmund King said: "Many motorists do not seem to have a clue what the signs mean.
"Some may be worried to venture past the M25 as they don't know what the LEZ is.
"Many seem to think it is linked to the Mayor's plan to tax 4x4s more for congestion. The signs do not make it clear that it does not affect cars."
Mr King added: "Rather than set up such a bureaucratic and complex scheme it would be more effective to target the minority of gross polluting vehicles."
He said questions from baffled road users had included whether it meant "beware of smog" and whether it was OK for asthma suffers to enter.
A Transport for London spokesman said it had received only three calls from people concerned about the scheme.
He said: "The Low Emission Zone systems have worked well today, London's roads are operating as normal, and Transport for London has received few calls from car drivers.
"Should the AA receive any calls from car drivers they need only advise them they are not affected and need take no action."
Green Party mayoral candidate Siān Berry said drivers have had plenty of warning about the scheme.
She said: "It's about time we had this brought in.
"The most important thing to me is Londoners' health and well-being and air pollution is one of the major causes of death in London at the moment."