Results from the 2011 census, released yesterday, showed that almost 70 per cent of Canberra residents usually travelled to work by car.

The proportion of people travelling to work by bus fell from 5.8 per cent to 5.6 per cent between 2006 and 2011. But there was an increase in the number of people walking or cycling to their workplace.

The results of a study to be presented at a conference this week indicate that travelling to work by car may contribute to weight gain.

Researchers from the Baker IDI Heart and Diabetes Institute found that people who did not use cars for commuting tended to gain less weight than those who did.

The four-year study of Adelaide residents found that people who did not drive to work put on an average of 1.2 kilograms, compared with 2.4 kilograms for people who drove every day.

Study author Takemi Sugiyama said it was possible that people in larger cities who drove to work would put on more weight because of longer travel times.

Mr Sugiyama said sitting still in a car appeared to have an adverse impact even on those people who did a large amount of exercise during their leisure time.

''Your muscles are not doing anything compared to a situation where you are standing in a bus or a train and your muscles are kind of active, contracting, doing something, expending energy,'' he said.

Mr Sugiyama said avoiding car use and undertaking physical activity may help people to maintain a healthy weight.

''Combining these two strategies - not using a car, if possible, and doing physical activity of 150 minutes per week or more - may be a kind of strategy we could examine as a potential way to address weight gain,'' he said.

The study will be presented at the Sports Medicine Australia Be Active 2012 conference in Sydney.

Labor has promised to boost public transport in Canberra by starting work on a Civic to Gungahlin light rail link if it forms the next ACT government.

Paul Mees, a senior lecturer in transport planning at the Royal Melbourne Institute of Technology, said low public transport usage in Canberra reflected policy failures.

''You need to get rid of your transport planners and get new ones in. You've got a proven failure of policy,'' Dr Mees said.

''It's a great irony about the ACT that it spends a very substantial amount of money on transport, including public transport, and gets nothing in return for it. Subsidy levels to public transport when compared to patronage are higher than in most other Australian cities and the attractiveness of the service to customers is low.

''Unless something is done to improve public transport across the whole of Canberra, not just for a select group of people, then no progress will be made.''