Google Maps will now warn drivers in London and other cities if they are going to enter a low-emission zone with fees or fines.
Several major cities have such schemes to keep polluting traffic out of their busiest areas.
But where such zones begin is often unclear – and can catch out tourists and occasional local drivers alike.
London’s Ultra Low Emission Zone (Ulez) covers an area with most of the city’s tourist hotspots and historical landmarks.
Drivers of older cars below modern emission standards have to pay £12.50 in the zone.
And, until it expands, in October, it applies in the same area as the separate £15 congestion charge.
The company says it supports efforts to cut traffic pollution in the most built-up areas.
And it announced the move, in March, alongside other planned changes, including making the “eco-friendly” option the default route.