Real-World Emission Reductions from Passenger Vehicles Over the Past 30 Years (1997)
In 1996, auto and oil industry groups claimed that modern cars emit 96 percent less pollution than 1960s-era cars built before emissions were regulated. These claims were misleading. In fact, 30 years of motor-vehicle pollution control regulations have reduced pollution from the entire US passenger vehicle fleet far less than one would expect. Here's why:
- A significant gap exists between emission standards and what cars emit in the real world. The primary sources of these excess real-world emissions are malfunctioning emission control equipment, aggressive driving behavior, and air conditioning operation. None of these "off-cycle" emissions are captured in the regulatory test cycle.
- Total miles driven by all passenger vehicles in the US (cars and light trucks) increased 2.7 times between 1965 and 1995, offsetting substantial amounts of the pollution reductions achieved on a per vehicle basis.
- The market share of light trucks (pickups, minivans, and SUVs) increased from 15% to 40% between 1970 and 1995. These light trucks have less stringent emission standards than passenger cars, especially for nitrogen oxides. In addition, the number of miles light trucks drive has increased at a much faster rate than the number of miles cars drive: 5.9 times for light trucks versus 2.2 times for cars.
- The claim that an individual modern car is 96% cleaner for carbon monoxide and hydrocarbons and 90% cleaner for nitrogen oxides than its precontrol-era (1960s) counterpart is overstated. Over its lifetime, the average emission rate for a car is much higher than its emission standard. A modern car will likely emit 4 times more carbon monoxide, 2 times more hydrocarbons, and 3 times more nitrogen oxides (Figure 1).
- For the entire US passenger vehicle fleet, emissions reductions have been considerably more modest or nonexistent. While emissions of hydrocarbons have been reduced by about two-thirds, emissions of carbon monoxide have dropped only a third, and nitrogen oxide emissions have actually increased more than a fifth over the past 30 years (Figure 2).
- The light truck fleet's share of US passenger vehicle emissions has increased by 1.7 times for carbon monoxide, 2.3 times for hydrocarbons, and 1.3 times for nitrogen oxides over the past 30 years. For the combined inventory of smog-forming pollutants (hydrocarbons and nitrogen oxides), the share contributed by the light truck fleet has doubled.
- The passenger vehicle fleet is still the largest single source of carbon monoxide and smog-forming pollutants nationwide. For hydrocarbons and nitrogen oxides separately, it is the second largest source, and its shares of these inventories have not changed appreciably since 1970.
With half of all Americans living in areas that violate national clean air standards, clearly emissions from the passenger vehicle fleet must be reduced. The main strategies that state and federal governments must adopt to reduce pollution from cars and trucks are
- lower emission standards to treat light trucks and cars equally
- implement well-run inspection and maintenance programs
- increase regulatory focus on emission control system durability and off-cycle emissions
- promote the introduction of truly advanced, intrinsically-clean vehicle technologies that have lifetime, real-world zero or near-zero emissions