Karen Lee, who addressed a forum of NSW government planners on Thursday, drew on her experiences in New York where commuter cycling had increased 289 per cent thanks to policies encouraging bike use.

Dr Lee, head of the New York City's Built Environment and Healthy Housing Program, has been working on urban planning measures to address diseases such as heart disease and diabetes, as well as obesity.

''The environments that we create through the work that we do in our societies is actually what determines the types of epidemics that we're going to see,'' she said.

Now just more than half NSW's population is active for at least 30 minutes a day, as recommended. But changing the way people moved around cities was found to improve activity levels by as much as 161 per cent, Dr Lee said.

Cycleways were being expanded in New York as part of its ''complete streets'' program, with roads being upgraded to include bus and bicycle lanes and allow room for pedestrian traffic alongside cars. It will introduce a bike-share system in May.

Dr Lee said mixed streets led to better economic outcomes, and had already eased congestion in America's most populous city.

''And it's not from making the roads wider for cars, it's actually from putting in all these other modes that become alternatives that people who are willing and want to do can now [use] safely.''

Other simple changes to encourage physical activity were found to be effective. Signs near lifts increased stair use by about 50 per cent, Dr Lee said.

''If the average American adult was to climb just two minutes of stairs a day, we could actually eliminate the average weight gains that we see in US adults.''