If half of all short trips during the summer months were done on two wheels instead of four, the Twin Cities would prevent nearly 300 deaths each year and save $57 million in medical costs, according to a study on biking and air pollution published Wednesday.

If trips of 5 miles or less were conducted by bicycle during the 124 best weather days of the year, 11 major cities in the Midwest would prevent 1,100 deaths from lung diseases, obesity and heart disease and save $7 billion annually.

Though the health benefits from reducing air pollution and increasing exercise are well known, the study is the first to estimate the combined effect of both on a city-by-city basis.

"If we were to make it as easy to bike as to drive a car, it would pay for itself a thousand times over," said Steve Clark, program manager for Transit for Livable Communities, a Minneapolis nonprofit that promotes alternative transportation.

The new findings come at a time when many cities, including Minneapolis, are trying to promote bicycling as a way to improve public health and reduce traffic congestion. They could be particularly useful for city planners and state legislators as they debate how best to spend shrinking dollars for transportation infrastructure, said the researchers. Just this week, Republicans in the U.S. Senate failed in their third effort in less than two months to eliminate federal money for bike paths, walking trails and other transportation enhancements.

The analysis was conducted by researchers at the University of Wisconsin and presented Wednesday at a major public health conference in Washington, D.C.

Effect of short trips

Jonathan Patz, director of the Global Health Institute at the University of Wisconsin and one of the authors, said the researchers wanted to estimate the change that would result from reducing short car trips. About 40 percent of all U.S. car trips are less than 2 miles -- yet mile for mile they produce far more air pollution than longer trips. Starting a car and driving it while the catalytic converter is still cold generates the greatest amount of emissions.

At the same time, heart disease, diabetes, obesity and lung conditions aggravated by air pollution are at epidemic levels in the United States. Each year 60,000 to 80,000 Americans die prematurely from air pollutants alone, Patz said.

The researchers combined data on transportation, emissions, population and health for 11 of the largest Midwestern cities, and they extrapolated what would happen if short car trips were reduced in the warmest six months of the year. They looked only at reduced ozone and large particulate matter, two of several pollutants produced in car exhaust.

They found that the effect on air pollution was modest, but the health impact was big.

"Applied across a large population, it has an effect in the millions of dollars," said Gregory Pratt, an expert on air pollution and public health with the Minnesota Pollution Control Agency (MPCA), who was familiar with the study and its methodology.

In fact, the true health benefits are probably underestimated, he said, because the study didn't include all the pollutants produced by cars, some of which can have an even worse health effect than the two that were included.

High biking rates

Increasingly, Pratt said, research is showing that the health benefits of biking outweigh the risks of greater exposure to air pollutants that can come with it.

The Twin Cities area is already experiencing some of those benefits because it has some of the highest biking rates in the country. In Minneapolis, about 4 percent of commuters get to work on a bicycle, according to the American League of Bicyclists, the 13th- highest rate in the country.

Since 2007 biking has increased by 33 percent in Minneapolis, largely as a result of a $25 million federal grant for building trails and bike lanes as well as adding racks. Minneapolis was one of four cities that received funding as part of a study on whether such an investment would result in less congestion, energy use, air pollution and better health, Pratt said.

"I think we should have safe [automobile] bridges," Patz said. But it's a mistake to "focus so much on costs and completely ignoring benefits."

The study was presented at the American Public Health conference in Washington, D.C., and published in Environmental Health Perspectives.

Josephine Marcotty • 612-673-7394