Swapping short car trips for walking or cycling could extend your life, according to a new study.

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University of Otago researchers found the health impacts of less car travel could be greater than you might have imagined.

More than half of car trips taken by New Zealanders are less than 5km, while 12 percent are under 1km.

The study's lead author, Anja Mizdrak, said swapping those for walking or biking could add between two and 25 "quality adjusted life years" per 1000 people depending on uptake. A quality adjusted life year represents represents a year lived in full health.

"New Zealand is highly car dependent - 79 percent of all self-reported trips are made by car and ownership rates are among the highest in the world - and only half of New Zealand adults meet national physical activity recommendations," she said.

This would result in healthcare cost savings of up to $2.1 billion for the country's population, while health gains would be comparable to those resulting from the tobacco tax.

It would also mean a 1.4 percent reduction in carbon emissions from road transport.

"Road transport also makes up 17.3 percent of the nation's gross greenhouse gas emissions, so it directly affects injury rates, physical activity and air pollution, and indirectly affects health through climate change.

"Switching short trips to walking and cycling is a good way to incorporate physical activity into daily life and reduce carbon emissions associated with vehicle use," Dr Mizdrak said.

The study, published in PLOS ONE, estimates health impacts, changes in health system costs, and greenhouse gas emissions associated with increasing active transport in New Zealand.

The researchers used data modelling techniques to estimate what the impact would be with uptake levels of 25, 50, and 100 percent.