After the end of World War II, Americans began moving en masse out of the cities and into the suburbs. These new suburbanites needed cars to make their daily commutes, and the nation soon started motoring on an unprecedented level. Along with the increase in cars on the road came an increase in fuel consumption -- and an unexpected rise in air pollution. California became the first state to establish clean air standards, due in part to the region's heat and natural topography that traps smog over congested cities like Los Angeles. By the 1940s, residents had already begun to suffer from watery eyes and respiratory problems as a result of the added pollution [source: Melosi].
By the 1960s -- at the objections of carmakers -- California began requiring various emissions control devices be placed on cars. This is what led to the advent of catalytic converters and the demise of lead-based gasoline. In 1970, President Richard Nixon signed the Clean Air Act into law. This act gave the federal Environmental Protection Agency (EPA) the authority to protect and improve the nation's air quality [source: EPA]. The Clean Air Act led to declines in carbon monoxide, hydrocarbon and nitrogen oxide emissions [source: Melosi]. The act has since undergone a few revisions -- several major revisions in 1990 and some minor ones in the years since.
The 1990 act proposed two national "tiers" that spelled out exactly how carmakers must reduce emissions. The Tier 1 standards went into effect in the mid-1990s, and are currently being phased out for stricter Tier 2 standards. Under the Tier 2 rules, SUVs, pickups, vans and large passenger vehicles are subject to the same national emission standards as cars. It also mandates the use of low-sulfur gasoline that will allow cars to run cleaner and says that diesel engines must abide by the same emissions standards as gasoline engines [source: EPA].
California's emissions standards are stricter than the federal ones. States can choose to follow the California standards if they choose, and several do. Cars are classified according to a number of acronyms:
- Low Emission Vehicle (LEV): releases fewer emissions than the average new car
- Ultra Low Emission Vehicle (ULEV): releases 50 percent fewer emissions than the average new car
- Super-Ultra Low Emission Vehicle (SULEV): releases 90 percent fewer emissions than the average new car
- Zero Emission Vehicle (ZEV): releases no emissions at all; includes electric cars and fuel-cell cars
On the next page, we'll examine how automakers comply with federal and state emissions regulations to help promote fuel efficiency and green driving. We'll also learn how eco-friendly driving technologies can help us reduce our carbon footprint.