A switch from driving to walking and cycling, as well as to public transportation, would bring health gains to the capital's population and cut output of the main gas blamed for global warming, according to the researchers led by James Woodcock, a scientist at the London School of Hygiene and Tropical Medicine.

Reliance on cars ``is not just bad for the environment, it's bad for our health,'' Woodcock told reporters yesterday in London at a briefing organized by U.K. medical journal The Lancet, which published the study. ``Energy-intensive, fossil fuel-based transport has many adverse health effects, while walking, cycling, and public transport reduce emissions and lead to public health benefits.''

Aside from cutting transportation emissions across London by 72 percent, shunning car journeys would decrease the risk of premature death in certain people by as much as 40 percent, Woodcock said. That cut is attributable to fewer road deaths and the lower chances of contracting cancer, diabetes and heart disease.

Under Livingstone's Climate Action Plan, the capital has a target to reduce its emissions of carbon dioxide, or CO2, by 60 percent by 2025, as part of London's contribution to fighting climate change. CO2 is the main greenhouse gas blamed for global warming, and United Nations scientists have warned emissions need to be stabilized and then reduced in order to avoid the worst ravages of climate change, such as droughts and heat waves.

At present, 59 percent of London car journeys range from 1 to 8 kilometers (0.6 to 5 miles) and represent an ``opportunity'' to switch to cycling, the scientists said. About 2 percent of current trips in London are made by bike.

Under a ``business-as-usual'' scenario, emissions from London's transport, excluding air travel, would fall by 10 percent by 2030 because of improvements in vehicle efficiency, the researchers said. Banning cars from inner London would cut emissions by 48 percent, still short of Livingstone's goal, while a total exclusion of cars from outer London also would slash transport's output of CO2 by 72 percent, they said. They didn't provide projections for 2025.

The challenge now is to encourage changes in policy, and change the public mindset by promoting cycling and emphasizing the health benefits of using more active modes of transport, said Andrew Prentice, another scientist at the London school, and a co-author of the paper.

One possibility would be to extend the scope of London's congestion charge zone into outer boroughs, Prentice said. On some days, a one-off charge of 50 or 100 pounds ($100 or $200) could be introduced ``to show people what the city would be like without traffic,'' he said.

Livingstone introduced the charge, now 8 pounds a day, in 2003 to reduce traffic tie-ups in the center and expanded it to west London this February.

``For over 50 years, public policy has favored private motor travel,'' Woodcock said. ``To change this, we need positive discrimination in favor of walking and cycling. The car is not a sustainable means of mass public transport.''