Vale Avenue was highlighted in the Transport Strategy as being of concern and having high levels of nitrogen dioxide.
The gas causes respiratory problems and the levels were only beaten in Fountain Street, St Peter Port, when measured between January and October 2012.
Residents said they were worried about the health implications. But rather than attributing it to traffic, they blamed the nearby power station.
Guernsey Electricity said its chimneys were designed to disperse the smoke as high as possible, but added there had been an increase in on-island generation.
Bernie Thompson, 61, has lived in the road for 34 years.
'Most pollution comes from the power station, although it is a busy road at times,' he said.
He has also seen 'oily, spotty molecules' on his car, which have been bad enough to burn through the paintwork, and that does concern him.
'God knows what comes out of the power station,' he said.
