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Understanding Low-Emission Vehicles

2/24/2012
Whether diesel- or gasoline-powered, all combustion engines expel noxious gasses such as unburned hydrocarbons and particulates into the air: the by-products of burned fuel that are discharged from the exhaust pipe into the atmosphere.

In the 1960s, government regulations were instituted to control automotive emissions and reduce the levels of pollution in the atmosphere. Over the years, engineering developments such as the three-way catalytic converter and computer-controlled electronic fuel injection have reduced automotive emissions today to less than five percent of what they were 40 years ago. Even now, the Environmental Protection Agency (EPA, www.epa.gov) continues to tighten air quality standards as technology improves. By 2009, all passenger vehicles will conform to standards that allow for less than one percent of the tailpipe emissions that were allowed in the 1960s. The EPA's newest standards are called Tier 2. California has separate emission standards for cars and trucks, known as LEV-II. For 2008, seven other states have adopted the California emissions standards: New York, Maine, Massachusetts, Pennsylvania, Rhode Island, Connecticut and Vermont. States that border these states may also sell California-certified vehicles.

Visit almost any new-vehicle showroom and you may hear quite a bit about so-called low-emission vehicles (LEVs). An LEV produces fewer emissions than the average vehicle on the road. This would have been a simple explanation just five years ago, but increased regulations and new powerplant technologies have led to the creation of several new categories of low-emission vehicles that have increasingly stringent standards. California, long the nationwide leader in toughening emission standards, created the CAL LEV (California Low-Emission Vehicle) program and established specific standards. As more states followed California's lead, the following definitions have gradually become accepted across the nation:

  • TLEV-Transitional Low-Emission Vehicle Early standard, phased out in 2004.
  • LEV-Low-Emission Vehicle This standard was the required average for all light vehicles sold nationwide for model years 2004 and beyond.
  • ULEV-Ultra-Low-Emission Vehicle Vehicles with this designation are 50 percent cleaner than the average new model-year vehicle.
  • SULEV-Super Ultra-Low-Emission Vehicle Vehicles with this designation are 90 percent cleaner than the average new model-year vehicle.
  • PZEV-Partial Zero-Emission Vehicle Vehicles that meet SULEV tailpipe emissions standards, have a 15-year/150,000-mile warranty and zero evaporative emissions.
  • AT PZEV-Advanced Technology PZEV Compressed natural-gas or hybrid vehicles that meet SULEV standards for tailpipe emissions, have a 15-year/150,000-mile warranty, zero evaporative emissions, as well as include advanced technology components.
  • ZEV-Zero-Emissions Vehicle Electric and hydrogen-fuel-cell vehicles that have zero harmful tailpipe emissions and are 98 percent cleaner than the average new model-year vehicle.
The latest hybrid-electric vehicles (those powered by a small internal combustion engine and one or more electric motors) typically fall under the AT PZEV classification. The vehicles are clean burning and nearly seamless in operation. Examples include the 2008 compact Honda Civic Hybrid and the midsize Nissan Altima, Toyota Camry and Prius hybrids. These vehicles also carry SmartWay designation. AT-PZEV classification also applies to the 2008 Honda Civic GX NGV (natural gas vehicle).

The advances in low-emissions technology are positively affecting SUVs as well. Traditionally heavy on weight and emissions, SUVs are customarily powered by large V-6 or V-8 engines. With hybrid technology, SUVs can produce lower emissions without feeling underpowered. For 2008, hybrid-electric SUVs include the 2-wheel drive (2WD) and 4-wheel drive (4WD) hybrid Chevrolet Tahoe, Ford Escape, GMC Yukon, Lexus RX 400h, Mazda Tribute and Mercury Mariner, the 2WD Saturn Vue Hybrid and the 4WD Toyota Highlander Hybrid. Four of these are SmartWay-designated vehicles with LEV-II SULEV classifications: Lexus RX 400h, Mazda Tribute Hybrid, Mercury Mariner Hybrid, and Toyota Highlander Hybrid. In 2WD, the Mercury Mariner Hybrid and Mazda Tribute Hybrid earn SmartWay Elite designation.

To capture the most stringent ZEV rating, a vehicle must be completely free of measured harmful emissions. On the drawing board at many automotive design labs today are hydrogen-powered or fuel-cell vehicles whose only by-product is water. Battery technology is advanced, but still does not offer enough range between charges to be competitive with either fossil fuels (gasoline or diesel) or hybrid-electric technology. Two ZEV models previously available in the United States were the battery-powered RAV4 EV from Toyota, and the EV1 from General Motors. Both are no longer on the market. The California Air Resources Board (CARB) in 2008 approved modifications to the ZEV Program to redesign it to affect 2015 and later model years.

To make it easier for consumers to find cleaner vehicles to buy and drive, the EPA created the Green Vehicle Guide. The greenest vehicles carry the EPA SmartWay Elite or SmartWay designations. SmartWay Elite designation is awarded to seven 2008 models that score 9 or better (on a 10-point scale) in each of the Air Pollution Scores and Greenhouse Gases Scores. These include the Ford Escape Hybrid, Honda Civic and Civic Hybrid, Mazda Tribute 2WD Hybrid, Mercury Mariner 2WD Hybrid, Toyota Camry Hybrid and Toyota Prius. SmartWay designation applies to dozens of 2008 models that score 6 or better on each for a combined score of 13. Consumers can look up a vehicle by type, by manufacturer, or by greenest vehicles, from model year 2000 to 2008. The site is at www.epa.gov/greenvehicles.