Every day, Americans are needlessly sickened from exposure to air pollution in the form of fine particles. Overall, health researchers estimate that fine particles, such as those found in diesel exhaust, shorten the lives of 70,000 Americans each year. Many more suffer the effects of particle-related respiratory and cardiovascular disease.

When during our day are we exposed to these particles? According to the California Air Resources Board, although we spend only about six percent of our day commuting to and from work, it is during that time when we receive over half of our exposure to utlrafine particles.

For the most part, the particles we breathe come from the diesel engines we encounter while driving or taking diesel-powered mass transit. According to the Transportation Research Board, one hundred and fifty million people—roughly half the population—travel to and from work in the U.S. daily. Most commuters drive, but many others take diesel-powered trains or city buses and ferries. Today's average commute lasts 25 minutes each way, and current trends indicate that our commutes, and therefore our exposures, are lengthening.

Legions of published, peer-reviewed studies have documented the increased exposure and resultant health risk from particles in and around nearby roadways. Using comparable instruments and research techniques as those employed by health researchers at major universities, Clean Air Task Force (CATF) investigated the exposure to diesel particles during typical commutes in four cities: Austin, Texas, Boston, Massachusetts, New York City, and Columbus, Ohio. In addition, CATF tested the air quality benefits due to emission control retrofits of transit buses in Boston and transit buses and garbage trucks in New York City.

CATF's investigation demonstrated that whether you commute by car, bus, ferry, train, or on foot, you may be exposed to high levels of diesel particles. Specifically, CATF documented diesel particle levels four to eight times higher inside commuter cars, buses, and trains than in the ambient outdoor air in those cities. In some cases, the ultrafine particle levels during the commutes were so high as to be comparable to driving with a smoker!

Several cities like Seattle, Boston and New York have purchased new cleaner transit buses and retrofitted many of their older buses and garbage trucks with effective emission controls. These emission controls are widely available today because U.S. EPA rules require them for new diesel engines starting this year. The only commutes where the researchers found little or no diesel exposure were commutes on electric-powered subways and commuter trains, on buses that have been retrofitted with diesel particulate filters or run on alternative fuels like compressed natural gas, and in cars traveling along routes with little or no truck traffic.

Although we may spend only 6% of our day commuting, that is when we get up to 60% of our daily exposure to harmful ultrafine particles
	Percent of Day Commuting	Percent of Daily Exposure to Harmful Particles
(SOURCE: CARB)

In Austin, Texas, CATF compared the particle levels in a car during a commute on Interstate 35 between Roundrock and Austin to the levels experienced in the same car traveling on the MOPAC (an expressway that follows the Missouri-Pacific railroad line). MOPAC provided a "no-truck" alternative for comparison because MOPAC prohibits truck traffic. CATF also compared the levels on I-35 to levels monitored in downtown Austin. Ultrafine particle levels on I-35 were consistently higher than on the MOPAC and black carbon levels were six times greater than at the downtown site.

CATF also documented similarly high levels of diesel pollution during car commutes in Boston, Massachusetts and Columbus, Ohio. See Findings on pages 10-11.

In-cabin particle exposures are much higher for commuters along routes with diesel trucks. The MOPAC highway (right) a no-truck alternative to I-35 (left) in Austin, Texas, had lower diesel pollution levels.

CATF's researchers investigated in-cabin levels of diesel pollution on city buses in Boston. We found the levels inside the conventional buses on average were about four times greater than the outdoor air. We then compared those levels to the levels monitored during commutes on similar buses in Boston that had been retrofitted with diesel particle filters. The monitoring demonstrated the filters substantially reduced the pollution in the buses.

CATF researchers measured high ultrafine particle levels on a conventional transit bus in Boston (left), while levels on a bus retrofitted with a particle filter were barely detectable (right).
Conventional and retrofit MBTA buses in Boston show the benefits of diesel particle filters to people in cars following behind. To view videos, move pointer over above images to display video controls.

CATF researchers observed that when a diesel locomotive pulls its passenger cars, the plume of diesel exhaust from the engine blows down onto the cars following the locomotive and invades the coaches. Pollution levels in these pulled coaches increased during the course of the commutes.

When a train is pushed, however, the diesel exhaust plume trails behind the locomotive and does not invade the coaches. The difference measured between the levels in a pulled versus a pushed train demonstrates the amount of in-coach pollution attributable to the diesel locomotive's engine. Measured ultrafine particle levels in the coaches of a pulled train were four times higher than the pushed train and as much as 17 times greater than the outdoor air. Regardless of whether the coaches were pulled or pushed, pollutant levels in the coaches skyrocketed when the trains arrived at an underground station. CATF documented diesel exhaust penetrating into the cabins of commuter trains through the open doors at the platform when the diesel locomotives entered underground rail stations in Boston.

When pulled by a locomotive (left), pollution from the engine invades the coaches behind. When the train is pushed, the pollution plume trails behind leaving in-coach levels low (right).

The plume of diesel exhaust from the engine invades the coaches.

The good news is that affordable technology is available today that can virtually eliminate commuter exposure to diesel particles on the road. The Diesel Particulate Filter (DPF) can reduce tailpipe emissions of these particles by up to 90 percent. EPA rules for new engines now mandate emissions consistent with this technology and the cleaner fuel it requires. These filters also work on the vast majority of existing diesel vehicles. CATF's study documented that particle concentrations did not increase above outdoor levels in cars following trucks and buses retrofitted with DPFs. In the interior of transit buses retrofitted with a DPF, passenger exposure from the bus exhaust was virtually eliminated. The following policies will be necessary for all Americans to enjoy a cleaner commute:

• State and local governments should clean up public fleets and fleets doing public work. States and local governments should take steps to clean up existing transit bus, school bus, garbage truck, and other public fleets. States should follow the lead of California, which is implementing a comprehensive diesel cleanup program, and New York, which recently required all state-owned or contracted fleets to use best available emission controls.
• States should create diesel cleanup funds. States should follow the lead of California (Carl Moyer) and Texas (Texas Emission Reduction Plan or TERP) in creating publicly-funded programs to provide the money necessary to retrofit existing dirty diesel fleets.
• Congress should fully fund federal diesel cleanup programs and states should use the money for diesel retrofits. The 2005 Transportation Bill (SAFETEA-LU) included $8.6 billion for Congestion Mitigation and Air Quality (CMAQ) projects. Congress gave priority to funding diesel retrofits because of their cost-effectiveness. It is up to local metropolitan planning organizations and state departments of transportation to award CMAQ monies for diesel retrofits. To date, only a few such projects have been funded at the state and metropolitan government level. In addition, in 2005, Congress passed the Diesel Emission Reduction Act (DERA) authorizing up to 200 million dollars a year over five years to pay for the cost of diesel retrofits. To date, however, Congress has failed to appropriate the money. To clear the air and create a healthier ride for hundreds of millions of commuters stuck in traffic with dirty diesels, Congress should fully fund DERA and state and local governments should prioritize awarding money to diesel retrofit projects.
• U.S. EPA should adopt an engine rebuild rule requiring long-haul trucks to upgrade their emission controls whenever their engines are rebuilt. Long-haul truck engines are typically driven for up to a million miles before they are replaced. Most of these engines are rebuilt several times during their useful lives. They emit the lion's share of diesel pollution that affects commuters on highways. Because these interstate trucks cross state borders, cleaning them up will likely require a federal solution. EPA should use it's authority under the Clean Air Act to require that their owners install best available controls whenever these engines are rebuilt.
• U.S. EPA should finalize its new engine rules for ferries and locomotives. U.S. EPA in the next year plans to issue emission standards for new marine vessels and locomotives. Over time this will mean significant improvement in emissions from these sources. In the near term, it should help demonstrate the viability and lower the cost of emission control solutions for existing ferries and locomotives.