More than 100 drivers have been asked to turn off idling engines in York to cut pollution levels.
But no one has yet been fined under anti-idling rules introduced last year.
About six hours and 45 minutes of vehicle engine idling time has been saved – with 105 drivers asked to switch off their engines by council enforcement officers.
Anti-idling patrols have been tasked with speaking to drivers who are parked up – but leave their car or van engine running.
Under rules launched last February, if drivers refuse they can be fined £20.
But a City of York Council spokesperson said fines would only be issued as a last resort – and the rules were introduced as a way to reduce idling rather than increase penalties.
Any driver of a vehicle idling on a road, in council car parks or on council land for more than two minutes could be asked to turn their engine off.
A poster campaign has also been rolled out across the city to discourage idling.