Studies Show Commuter Trains Don’t Improve Air Quality

Published August 1, 2004

Recent studies in Denver, Dallas, and other cities show rail transit is a particularly ineffective solution to air pollution problems. Rail transit, the authors conclude, has an insignificant effect on air quality, and it actually increases the emissions of some important pollutants.

Dallas Rail Line Costly, Ineffective

A study by Dallas’ transit agency, reported in the June 15 Dallas Morning News, concluded a proposed new light-rail line would reduce regional carbon monoxide emissions by less than one one-hundredth of a percent. Even a larger reduction wouldn’t be important, since Dallas already complies with federal carbon monoxide standards.

The proposed light-rail line would, however, hurt regional air quality by increasing nitrogen oxide emissions by 42 tons, nearly one-tenth of a percent. Dallas already is out of compliance with federal standards for ozone, which is created when nitrogen oxides combine with other pollutants in the air. The light-rail line would force the region to impose more expensive pollution-reduction measures on local power plants that produce the electricity needed to run it.

Denver Rail Would Increase Carbon Monoxide

Similar results were found by the Denver Regional Council of Governments (DRCOG) for proposed new rail lines (known as FasTracks) in that metropolitan area. By attracting less than one-half percent of auto drivers out of their cars, the rail lines would reduce carbon monoxide and particulate emissions by less than 1 percent. They would increase nitrogen oxide emissions by nearly 3 percent.

The Denver plan includes three light-rail lines, three commuter-rail lines, and one bus-rapid transit line. The light-rail lines would produce almost twice as much nitrogen oxide as all the cars taken off the road by the plan, and the commuter-rail trains would produce four times as much nitrogen oxide as the cars they replaced. Nitrogen oxides produced by the buses would be insignificant. Like Dallas, Denver complies with all federal air quality standards except for ozone.

Denver’s proposed light-rail lines would be quite costly. The June 18 Denver Business Journal noted, “FasTracks will cost the average Denver-area resident $160 in 2025, yet DRCOG says FasTracks will give average metro-area residents just six new transit rides a year. That’s a cost of $26 a ride! While it will make certain members of the Chamber of Commerce rich, it certainly won’t do anything about congestion or air pollution. A vote for FasTracks is a vote for higher taxes, congestion, and gridlock; a vote against it is a vote for better transportation solutions that don’t require new taxes.”

Rail Unpopular with Commuters

The air quality argument works against rail transit because it does not attract a significant number of people out of their cars. Denver’s plan calls for building 120 miles of rail transit, but DRCOG estimates doing so will reduce auto driving by less than half a percent.

Most suburban rail riders drive to the train stations. Cars pollute the most before they are warmed up. Someone who drives two miles to a park-and-ride station and then rides light rail eight miles emits about as much pollution as the commuter who drives all 10 miles.

The other time cars pollute more than usual is in stop-and-go traffic. Since rail transit doesn’t get many cars off the road, it doesn’t alleviate traffic congestion. But it does consume funds that could otherwise be spent to reduce congestion.

Traffic Technology Mitigates San Jose Pollution

The city of San Jose recently spent less than one million dollars synchronizing traffic signals on its most congested streets. Traffic engineers calculate that move reduced auto emissions by 5 to 15 percent, depending on the pollutant, and also saved motorists nearly half a million gallons of fuel and thousands of hours each year.

Amortizing the cost of signal synchronization over 10 years results in an estimate of roughly $1,000 per ton of reduced emissions. By comparison, many rail projects spend well over $1 million per ton of reduced emissions.

The problem of automotive pollution has been falling and will continue to fall because of federal regulation of new cars. Americans drive about three times as many miles as we did 35 years ago … yet our vehicles produce less than half as much pollution.

The federal government continues to tighten the standards for new cars each year, and standards for sport-utility vehicles (SUVs) are now the same as for cars. As a result, the nation’s motor vehicle fleet is becoming about 10 percent cleaner each year. Since we drive about 2 percent more each year, we enjoy an 8 percent annual net reduction in auto emissions.

Buses Cheaper, More Convenient

While it won’t do much more to relieve congestion, bus-rapid transit can provide much better transit service at a far lower cost than rail transit. Bus-rapid transit consists of running buses on rail speeds and frequencies. Given equal speeds and frequencies, studies show buses can attract as many new transit riders as trains.

The General Accounting Office says bus-rapid transit can go faster and cost less than rail transit. Denver’s transit agency plans to run bus-rapid transit buses every two to four minutes at an average speed of 51 miles per hour. Light-rail’s average speed is only 24 miles per hour, and commuter rail is 41 miles per hour; neither can operate as frequently as bus-rapid transit. Finally, despite better service, bus-rapid transit costs less per rider to operate and far less to build than rail transit.

Randal O’Toole is a senior economist with the Thoreau Institute and author of The Vanishing Automobile and Other Urban Myths. His email address is [email protected].

For more information …

The 96-page final report of the Denver Regional Council of Governments, “Review of the RTD FasTracks Plan,” published April 21, 2004, is available online at

The Thoreau Institute’s Web site at offers additional information on light rail and other urban issues.