· People in busy roads more likely to be ill, says study · Lack of traffic promotes sense of community

Mrs A lives in Dovercourt Road in north Bristol and considers five people on her street as friends. But Mrs B, who is roughly the same age and lives round the corner in a very similar house in Muller Street, has only one friend.

The difference, says a study, has nothing to do with personality, but is because of the weight of traffic. Fewer than 150 vehicles a day pass down Dovercourt Road, compared with more than 21,130 a day on Muller Street.

New research, based on interviews with households on three Bristol streets, has found that people who live with high levels of motor traffic are far more likely to be socially disconnected and even ill than people who live in quiet, clean streets.

It confirms a study done by a British academic in San Francisco in 1969. This found the weight of traffic in urban areas largely determined people's quality of life and also identified a major erosion of community on busy streets. The Bristol study is the first time that research has been conducted in Britain.

Joshua Hart, a researcher at the University of the West of England, Bristol, looked at Muller Street, Filton Avenue and Dovercourt Road, three streets with very different traffic flows.

He dubbed them Heavy (Muller Street), Medium (Filton Avenue), and Light (Dovercourt Road) streets and mapped the movement of residents. People were asked to identify their social contacts, and say what they considered to be their "home".

He found wide differences in community interaction and a serious deterioration of community life on busy roads. On average, residents on Heavy Street had about one fifth the number of local friends and only half the number of acquaintances compared with the people living in Light Street.

People there admitted to knowing very few others in the road, had very few friends on the other side of the street and seldom crossed over. "It's hellishly busy. The buses and lorries shake the house and the air pollution can be quite bad," said one man. Residents on Light Street, however, reported that they felt a sense of community, frequently popped in and out of each others' homes and said that they felt personally responsible for a much larger area than residents on Heavy Street.

More than half the people interviewed said they felt "at home" in other people's houses. "People stay for a while and put down roots," said one man. "We look after each other," said another.

Hart also found people were taking extreme measures to adapt to the noisy, dirty environment on Heavy Street. Residents largely lived in the back rooms of their houses and many chose dark or black curtains to conceal the soot build-up from vehicles.

They kept their front windows closed, did not allow children to play in the street and usually accompanied them to school, he said.

Heavy Street also found people less likely to care for their street. "The whole street needs knocking down and rebuilding" was one comment. "People argue and shout regularly."

It could not have been more different on Light Street, reported Hart. There, very few people felt the need to build a fence or a wall in the front garden, and most people had their windows open.

Residents there reported almost three times the number of gathering spots compared with Heavy Street.

"The primary influence on social deterioration is the external effect of traffic, not any possible personality differences among residents of the three streets," he concluded.

"Growing car dependence is creating an epidemic of deteriorated mental and physical health associated with air and noise pollution, inactivity and road deaths and injuries.

"It seems that community and quality of life have been neglected whilst planning and transport policies have led to a massive growth in motor vehicles in the UK," said Hart.

"More than 5 million extra cars are expected on the UK's roads by 2031, and these findings point to an urgent need for the government to provide healthy residential environments and to stem traffic growth by investing in public transport, walking and cycling in order to avoid many more local communities being impacted."