Building more roads does NOT reduce congestion in the long run. 
 

• In the last decade, the one-third of metro areas that added the most road space per person experienced a 6.5 percent increase in rush-hour congestion, compared to a 7.2 percent increase in the metro areas that added the least road capacity. The low road building areas had higher population growth than the high road building areas, eliminating population growth as an explanation for the differences between the two sets of areas. 
• Travel delay is actually higher on average in the 23 metro areas that built the most roads. In the long run, this encourages additional development nearby, and that leads to even more traffic.
• According to a U.S. Department of Transportation study, as much as 69% of the growth in driving between 1983 and 1990 was caused by factors influenced by sprawl. These factors include the same people driving farther, as well as a decrease in carpooling and a switch from biking, walking, or transit to driving.
• Our cumulative road-building and land development decisions undergird the steady rise of U.S. vehicle miles traveled (VMT) in the second half of the twentieth century.  From 1970 to 1990, VMT doubled from 1 to 2 trillion per year and Americans traveled 2.6 trillion miles in 1998.

There is strong evidence that impacts from highways cause a significant number of public health problems.  The consequences of vehicle travel and dependency include: 
 

• Public safety:  Poorly designed transportation networks discourage physical activities such as walking and biking, increases pedestrian injuries and fatalities, and increases the risk of car crashes.
• Air quality: In 1991, air pollution from highways is estimated to have caused between 20,000 and 46,000 cases of chronic respiratory illness.
• The Centers for Disease Control and Prevention (CDC) conducted a study that found that decreased citywide use of automobiles in Atlanta during the 1996 Summer Olympics led to improved air quality and a large decrease in childhood emergency room visits and hospitalizations for asthma. 
• Water quality: 95% of the lead found in the Chesapeake Bay is deposited from air pollution.  Loss of vegetation increases runoff and flooding.
• Greenhouse gas emissions and global climate change: In 1997, the transportation sector emitted 32% of US CO2 emissions from fossil fuels, or 473.1 million metric tons of carbon.
• Traffic noise: An estimate for 1980 indicated that 37% of the U.S. population was exposed to highway noise great enough to cause annoyance, defined at greater than 55 decibels

The United States is losing wilderness, open space, natural areas and farmland to unplanned and unchecked development at a rapid pace.
 

• From 1982-1992, the rate of open space loss was 1.4 million acres a year; from 1992-1997, the annual rate of loss was 50 percent higher at 2.1 million acres.
• In the U.S., 91,357 miles of new highway were built between 1990 and 1997.
• A 1994 study by the American Farmland Trust showed that urban development already has consumed nearly a third of the country’s most highly productive farming regions.

Transportation infrastructure has a permanent, often destructive impact on wildlife and the natural environment.
 

• Habitat destruction: The actual construction of a road, from clearing to paving, will result in the death of any slow-moving organisms in the path of the road. Obviously, trees and any other vegetation will be destroyed, as well as any organisms living in that vegetation.
• Once built, a road acts a barrier for migrating wildlife.  Species that will not or cannot cross roadways are isolated from valuable feeding, wintering or birthing habitat. When roads restrict movement, they also bar gene flow where individuals are reluctant to cross for breeding.
• Roadkill is the greatest directly human-caused source of wildlife mortality throughout the U.S. Over one million vertebrates per day are killed in vehicle collisions on U.S. highways.

Transportation is by far the largest consumer of petroleum products in the U.S., accounting for two-thirds of our overall oil consumption.  We can reduce our dependence on foreign oil by reducing vehicle trips.
 

• Transportation alone consumes more oil than the U.S. produces, and also more oil than we import each year.
• The average American citizen uses three times as much energy for transportation as the average citizen of Western Europe and five times as much as the average Japanese citizen. 

Additional roads make places more expensive to live as transportation costs and maintenance bills increase prices and taxes. 
 

• In many cities, families can pay more for transportation than housing.  In Houston, TX, transportation expenditures average $8,840, or 22.1% of expenditures.  High transportation costs hit the poor the hardest as these costs represent a greater share of household income.

Roads alter the chemical environment.  Maintenance and use of roads contribute at least five different general classes of chemicals to the environment.

• Heavy metals - gasoline additives
• Salt - de-icing
• Organic molecules - dioxins, hydrocarbons
• Ozone - produced by vehicles
• Nutrients - nitrogen

Roads provide opportunities for invasive species to spread by:
 

• providing habitat by altering conditions
• stressing or removing native species; and
• allowing easier movement by wild or human vectors.

Conclusion 
• The Harvard School of Design has calculated that our roads and their various fringe effects (air, water, noise pollution) have an impact on about 1/5th of U.S. land area.