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Stephanie Corson

Private Transportation vs. Mass Transit:
The Environmental Aspects

Air Pollution: The Basics

For the last few decades, air pollution has become an increasingly evident problem. Many of the pollutants in the air such as carbon monoxide, carbon dioxide, nitrogen oxides, and hydrocarbons are produced by automobiles. The Department of Health, Education and Welfare has estimated that automobiles account for approximately 48% of the carbon monoxide, 32% of the nitrogen oxides, and 59% of the hydrocarbons in the atmosphere. These pollutants have an adverse effect on the environment and on humans. A mass transit system is more beneficial to the environment because it reduces the amount of pollution released into the air by providing an alternative to private transport that can be used by many. Mass transit systems are also more energy efficient modes of transportation than automobiles.

Carbon monoxide is a chemical compound of carbon and oxygen. It contributes to the greenhouse effect and causes health problems. In high concentrations, it tends to replace the oxygen in the bloodstream, which reduces the delivery of oxygen to body tissues. This impairs perception and thinking, slowing reflexes and causing drowsiness. Prolonged exposure to large quantities can cause unconsciousness and death. It may also impair the nervous system or heart function. Carbon monoxide is also a pollutant that contributes to the formation of smog. Each car gives off an average of approximately two-thirds of a ton of carbon monoxide per year.

Automobiles are one of the largest sources of man-made carbon dioxide. Burning just a single tank of gasoline produces 300-400 pounds of carbon dioxide. It is also the main greenhouse gas. Too much of it may cause temperatures to rise, as it is a gas that tends to trap heat in the atmosphere. It is responsible for approximately 49% of global warming.

Nitrogen oxides are gases composed of nitrogen and oxygen. They contribute to the greenhouse effect as well as to the formation of smog. When they combine with water, nitric acid (a component of acid rain) is formed. Nitrogen oxides are the second major source of acidifying compounds in acid rain, next to oxides of sulfur. Nitrogen oxides are toxic to vegetation. They can also increase susceptibility to viral infections such as influenza. In addition, they may irritate the lungs and cause bronchitis.

Hydrocarbons are also a component of smog. The photochemical reactions between hydrocarbons and nitrogen oxides produce the many secondary pollutants that reduce visibility and cause eye and nose irritation. They are precursors of ozone, which irritates respiratory tracts and eyes, decreases the lungs' working ability, and causes both coughing and chest pain.

Automobile pollution comes primarily from the engine, the crankcase, and the exhaust. Engine fumes are the main source of hydrocarbons, carbon monoxide, and nitrogen oxides. In a car without emissions control equipment, engine fumes account for approximately 100% of carbon monoxide and nitrogen oxide emissions, as well as 55% of hydrocarbon emissions. Another 20-25% of hydrocarbon emissions come from the crankcase, while the final 20-25% come from the evaporation of gas in the fuel tank and carburetor. Carbon dioxide is emitted from the tailpipe as exhaust.

Some byproducts of automobiles, such as water vapor, are considered relatively harmless, but others can have a serious impact on the surrounding environment. They may change weather patterns, cause the greenhouse effect, or result in the formation of smog or acid rain. Ozone, which can make eyes water and which irritates the linings of the nose, throat, and lungs, is produced by a chemical reaction of sunlight and car exhaust fumes.

The Legacy of Automobiles: Smog, Acid Rain, and the Greenhouse Effect

The greenhouse effect is what it happens when gas molecules in the atmosphere, such as carbon dioxide, block heat from escaping the earth's surface. This occurs naturally to some extent because of the natural composition of gases in the atmosphere. But when tons of man-made pollutants are released into the atmosphere, the natural composition of gases is changed. The excess carbon dioxide could cause more heat to be trapped, thus increasing the overall temperature of the earth. Sea levels could rise due to the melting of the polar ice caps. Obviously, this would lead to extensive flooding of coastal regions. In addition, since many plant and animal species are adapted to specific climatic conditions, global warming would force them to migrate further north (and further south in the southern hemisphere). Whenever such a migration is not possible because of natural or man-made barriers, these species would go extinct.

Smog is an urban air pollution composed of exhaust emissions, smoke, and other gases. It contains pollutants which affect people's health. Some, such as carbon monoxide, are toxic enough to cause serious illness. Others can cause coughing, wheezing, and chest discomfort at relatively high concentrations. It is also harmful to crops and reduces visibility. Higher temperatures in the surrounding atmosphere, such as would be produced by the greenhouse effect, could lead to higher levels of smog. Smog itself can create a blanket over cities that traps heat, thus producing a kind of mini-greenhouse effect. In the United States, automobiles contribute more than one half of the pollutants that form smog.

One very evident case of the damaging effects caused by smog took place in the Los Angeles basin. The large number of cars there emitted a great quantity of pollution fumes into the air, and the mountains surrounding the city kept these fumes from spreading out and away from the city. Because of the buildup of these pollutants, Los Angeles experiences approximately 120 days of smog per year.

Acid rain is another result of pollution. Car emissions fill the air with nitrogen oxides. Some of these gases attach to particles in the air and fall to the earth as dry deposition. However, the majority of them mix with the moisture in clouds to form nitric acid. This acid then falls with the remainder of the water in the clouds as acid rain. The acid rain poisons trees, crops, and other plants. These acids also build up in rivers and lakes, killing the fish and other creature living there and polluting the water.

Acid rain kills trees and other plants by changing the chemical balance of the soil. It can deplete the soil of nutrients essential for the growth of the plants, elevate the levels of toxic metals in the soil, and alter the normal growth process. Acid rain is also harmful to non-organic materials. It damages the paint on cars and wears away stone. Marble and limestone are particularly susceptible to acid rain, so any buildings or monuments containing those types of stone wear away at a much faster rate than normal. Acid rain may also be the cause of rusted steel in bridges and corroded buildings.

The United States has had laws to control air pollution for the past thirty-five years. The Clean Air Act passed in 1963 was designed to stimulate state and local pollution control activity. In an amendment to the Clean Air Act passed in 1970, the federal government set uniform national ambient air quality standards for pollutants. It also called for a further reduction in hydrocarbons and carbon monoxide of 90% by 1975. Imposing the standards set in this amendment has resulted in the reduction of hydrocarbons and carbon monoxide by 96%, and nitrogen oxides by 76%. In 1990, Congress amended the Clean Air Act to reduce the emissions that produce acid rain by approximately 50% by the year 2000.

From an Environmental Point of View: Cars vs. Mass Transit

Emissions standards for cars were first imposed in California in 1965. An amendment to the Clean Air Act in 1965 authorized the writing of national standards for emissions from all new motor vehicles sold in the United States. The result of this was the requirement of exhaust emission control devices on cars nationwide, starting with 1968 models. Control of nitrogen oxide emissions began in 1971. A drawback to emissions control is that while it can significantly reduce the amount of pollutants produced by automobiles, it also causes a rise in the cost of the cars along with a decrease in the amount of mileage. Even with emission controls, automobiles that are poorly maintained still produce many pollutants, as poor maintenance inhibits the effectiveness of such controls. Also, the lower emissions per new vehicle have been offset by the vastly increased number of vehicles on the road. Still, there has been an actual decrease in concentrations of carbon monoxide in urban areas.

A mass transit system would be a very effective way to help counter the air pollution problem. Obviously, if the majority of people used a public transport system instead of private vehicles, there would be less pollution produced. It is also more energy efficient. A rail transit system would also be cheaper and faster to build and expand than roads are. It has the added benefit of providing access to a mode of transportation for the non-driving public.

A car occupied by one person produces on average 2.06 grams/passenger-mile (g/pm) of nitrogen oxides for work trips. A fully occupied transit bus, on the other hand, would produce 1.54 g/pm, while a fully occupied rail transit system would produce only .47 g/pm for the same distance. Similarly, the car occupied by one person would produce 15.06 g/pm of carbon monoxide and 2.09 g/pm of hydrocarbons. The bus would produce 3.05 g/pm and .2 g/pm of the same pollutants, respectively. From an environmental point of view, trains are the best form of transportation: a full passenger train produces only .02 g/pm pf carbon monoxide and .01 g/pm of hydrocarbons.

A bus with as few as seven passengers is more fuel efficient than the average automobile used for commuting. The fuel efficiency of a fully-occupied bus is six times greater than that of the average commuter's automobile, while the fuel efficiency of a fully-occupied rail car is fifteen times greater than that of the average commuter's automobile. A single person who commutes via a transit system instead of driving alone will save 200 gallons of gasoline per year. A 10% nationwide increase in transit ridership would save 135 million gallons of gasoline per year. This fuel efficiency results in personal savings and in a cleaner environment for all.

For people who would like to help make the environment a cleaner place, mass transit is an ideal solution. It may not be free to build, but in the long run it is healthier for everyone. Less pollution will make the air cleaner, and fewer resources such as gasoline will be used. Many cities do have viable mass transportation systems, and the people who use them are, on the whole, well-satisfied.

References and Further Reading

American Public Transit Association. Information on the web at http://www.apta.com

Baines, John. Acid Rain. Austin: Steck-Vaughn, 1989.

Crouse, William & Donald Anglin. Automotive Emission Control. New York: McGraw-Hill Inc, 1983.

Haynes, John & Mike Stubblefield. Automotive Emissions Control Manual. Haynes North America, 1992.

Lyman, Francesca. The Greenhouse Trap. Boston: Beacon Press, 1990.

Patterson, D.S. & N.A. Henein. Emissions from Combustion Engines and Their Control. Michigan: Ann Arbor Science, 1972.

Regens, James & Robert Rycroft. The Acid Rain Controversy. Pittsburgh: University of Pittsburgh, 1988.

Stille, Darlene. The Greenhouse Effect. Chicago: Chicago Press, 1990.

Stille, Darlene. Air Pollution. Chicago: Chicago Press, 1990.

Watson, Bates, & Kennedy. Air Pollution, the Automobile, and Public Health. Washington , D.C.: National Academy Press, 1988.

Wekesser, Carol. Water: Opposing Viewpoints. San Diego: Greenhaven Press, 1994.

White, Lawrence. The Regulation of Air Pollutant Emissions from Motor Vehicles. Washington D.C.: American Enterprise Institute, 1982.

Willis, Terri. Cars: an Environmental Challenge. Chicago: Chicago Press, 1992.

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