Australian experts say the study is intriguing, but have warned against jumping to conclusions.
Air pollution and noise can be two of the downsides of living close to a major road.
And new research published in the Lancet shows it may come with an added risk.
A study of two million people in Canada found around 10 per cent of dementia cases in urban areas could be linked to exposure to heavy traffic.
Living within 50 metres of a major road increased the risk of dementia by seven to 11 per cent.
At 100 metres, the increased risk was four per cent.
Dr David Reynolds from Alzheimer's Research UK says the research is significant.
"This research shows, I think for pretty much the first time, there is a link between living near a busy main road and having an increased risk for dementia, which I think shows this could be a new risk factor we hadn't really considered before."
Alzheimer's Australia's Chief Medical Advisor, Associate Professor Michael Woodward, says the research is intriguing, but far from conclusive.
"I wouldn't jump to the conclusion that we need to move away from roads to reduce our risk of Alzheimers, there are many possible explanations for this link. It might be something in air pollution, it might be traffic noise, socio-economic factors that lead people to need to buy cheaper housing nearer to busy roads. "
More than 350,000 Australians are living with dementia - and the rates are increasing.
The disease gradually robs people of their memories and brain function.
However scientists still don't fully understand its origin.
For now, Professor Woodward says there are simple things we can do to reduce the risk ..
"Be active, eat well, keep socially active, avoid excess alcohol, avoid cigarette smoking. There are things we can do right now. Moving away from a road would not be the first priority, on the basis of this one very interesting, but nevertheless, not conclusive, study."
