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Status Report, Vol. 41, No. 2 | February 25, 2006 Subscribe

Proposed revision of fuel economy standards would be a win for safety

Ever since Congress imposed corporate average fuel economy requirements in the 1970s, automakers have been complying by downsizing their vehicles so they use less fuel and/or by using sales of smaller, lighter, and more fuel-efficient vehicles to offset what's consumed by their bigger vehicles.

The problem is that these choices have compromised safety. Smaller, lighter vehicles generally are less protective of their occupants in crashes.

This built-in contradiction between safety and fuel economy may be on the verge of disappearing, or at least diminishing. The National Highway Traffic Safety Administration (NHTSA) is proposing a standard for SUVs, vans, and pickup trucks that, besides imposing somewhat tougher fuel economy requirements, would restructure the way fuel economy is calculated for compliance purposes. The effect would be that manufacturers would have to improve the fuel efficiency of all of their vehicles.

"Both conserving fuel and enhancing occupant safety are worthy goals," says Institute president Adrian Lund. "The problem is only when they work against each other. What NHTSA is saying in its proposal is that automakers will have to meet increasingly tougher fuel economy requirements without compromising safety by downsizing their vehicles. Instead they'll have to consider a compliance strategy they've largely resisted in the past — applying technologies to improve fuel economy."

Human costs of downsizing

The safety disadvantages of small vehicles are inherent. Because they're lighter, they're at a disadvantage in collisions with larger vehicles and even in many single-vehicle crashes. There's less structure to absorb crash energy before it can harm occupants, so deaths and injuries are more likely to occur.

Study after study confirms that when vehicles are made smaller and lighter the risks for their occupants go up. For example, the National Academy of Sciences reported in 2001 that "the downweighting and downsizing that occurred in the late 1970s and early 1980s, some of which was due to [fuel economy] standards, probably resulted in an additional 1,300 to 2,600 traffic fatalities in 1993."

An earlier study by researchers at Harvard University and the Brookings Institution estimated that downsizing vehicles was "associated with a 14 to 27 percent increase in occupant fatality risk." These researchers projected that federal fuel economy standards are "responsible for 2,200 to 3,900 excess occupant fatalities over the 10 years of a given model year's use."

More studies, including NHTSA's own, address the safety consequences of regulatory actions that increase sales of small, light vehicles. The agency's current regulatory proposal is designed to unhook such consequences from ongoing efforts to improve fuel economy.

How the system would work

Federal fuel economy requirements in place for 30 years have applied to each automaker's entire fleet. It's the average economy across a fleet that counts, so manufacturers can offset sales of heavier, less efficient vehicles by increasing sales of lighter ones that use less fuel.

Under the proposed standard, NHTSA would continue to set overall fuel economy requirements for each manufacturer's fleet of SUVs, vans, and pickup trucks in each model year, just as the agency has for years. The big change under the proposal is that these targets wouldn't be applied uniformly across a manufacturer's fleet. Nor would all manufacturers meet the same targets. Instead the fuel economy of each manufacturer's fleet would depend on the size of the vehicles that are sold.

SUVs, vans, and pickups would be sorted into six categories, based on size, and the vehicles in these categories would be subject to different targets. Until the 2011 model year, manufacturers could choose whether to comply with this option or meet fuel economy requirements the way they have in the past, by ensuring that their fleets meet an overall target. For the 2008 model year, the target would be 22.5 miles per gallon, up from the current 22.2. Then the requirement would rise to 23.1 (2009) and 23.5 (2010) miles per gallon. In the 2011 model year all manufacturers would have to meet the size-based variable requirements NHTSA is proposing.

The agency estimates that this proposal would save at least 6 billion gallons of fuel over the life of 2008-10 SUV, van, and pickup models, compared with an absence of federal fuel economy standards. Meeting the 2011 requirement would save an estimated 4.1 billion gallons.

"These savings would be achieved without the safety downsides of the past," Lund says. "There still could be room for automakers to tinker with the sizes and weights of their vehicles, but this would be a much less attractive option than it has been."

Downsizing vehicles to meet the new standard would be discouraged because smaller vehicles would have to meet tougher requirements. Instead of downsizing, the manufacturers would be forced to apply fuel-saving technologies to meet the targets NHTSA has laid out for 2008 and later models. For example, a manufacturer could turbocharge small, more fuel-efficient vehicle engines to achieve adequate performance instead of using turbochargers, as many automakers do today, mostly to boost the power of bigger engines even higher.

Potential to thwart the proposed system

Manufacturers who want to avoid using technologies like turbocharging to improve fuel economy might try to reduce the weights of their vehicles while maintaining size to avoid pushing the vehicles into new categories that have tougher fuel economy requirements. This would compromise safety because reducing vehicle weight reduces, on average, how well a vehicle protects its occupants in crashes.

The consequences would be worse if the weight reductions were taken among the smallest and lightest SUVs, vans, and pickups. This is because the safety benefits of size and weight diminish among vehicles weighing more than about 4,000 pounds (see "Passenger vehicle size, weight, fuel consumption and occupant safety," April 6, 2002).

Another option would be to downsize a vehicle within a category — that is, make it smaller to use less fuel but only to the extent that the downsizing wouldn't push it into another size-based category with a tougher fuel economy target.

"These options wouldn't be good from a safety standpoint, but at least there's a built-in limit to how much downweighting or downsizing a manufacturer could pursue," Lund points out.

Some thwarting of the intent of NHTSA's proposed standard could even enhance safety. If a vehicle were redesigned to make it bigger so it could meet an easier fuel economy target, the occupants would reap the protection afforded by the extra size (and probably extra weight) in a crash.

Most opportunities for getting around what NHTSA intends stem from the plan to categorize vehicles by size for compliance purposes. The six categories are what give automakers room to change the sizes and weights of vehicles without changing their fuel economy targets. To discourage this, the Institute advises NHTSA to replace the categories with a continuous system under which each vehicle size increment would trigger an incremental change in the fuel economy requirement. Such a system could be adopted with a minimum of additional research.

Whole vehicle fleet could be affected

NHTSA's proposal addresses the fuel economy of SUVs, vans, and pickup trucks, not cars, but there could be some effects for cars too. In some cases, smaller cars have been adapted to meet the classification requirements — and the less stringent fuel economy requirements — that have prevailed for SUVs, vans, and pickups. This has allowed manufacturers to sell more big vehicles while still meeting average fuel economy targets set by the federal government. However, the incentive to do this would be greatly reduced under NHTSA's proposed standard.

Agency doesn't set car targets

Fuel economy requirements for cars always have been set separately from those for SUVs, vans, and pickups. Congress, not NHTSA, sets the targets for cars and establishes how the agency will calculate compliance. NHTSA sets the targets for the other vehicles, and this target has been less stringent than the one for cars — 22.2 miles per gallon compared with 27.5 for cars this year. However, by the 2010 model year NHTSA's proposed target of 27.8 miles per gallon for small SUVs, vans, and pickups would be tougher than the current standard for cars.

"The agency's plan represents the federal government's first thoughtful effort to enact energy policy that also takes into account the safety of millions of motorists on U.S. roads," Lund concludes. "When this plan goes into effect and members of Congress begin to see how it works for SUVs and pickup trucks, we hope they'll apply the same regulatory approach to cars. Then we can maintain safety even as we achieve enhanced fuel economy across the vehicle fleet."

NHTSA says it expects to issue a final standard on fuel economy for SUVs, vans, and pickup trucks sometime later this year.

Relationships between vehicle weight and driver deaths and fuel consumption


The highest death rates and lowest fuel consumption are for the lightest vehicles. Heavier vehicles have lower death rates and consume more fuel per mile, but the safety benefits of the added weight diminish as vehicles get heavier and heavier (meanwhile fuel consumption continues to increase). The optimum fleet mix to enhance safety would include fewer of the heaviest vehicles as well as the lightest ones.

Note: The relationships between death rates and vehicle weights shown above reflect fatal crashes of 1999-2003 models during 2000-04. The rates are adjusted to account for some differences in driver age and sex within and between vehicle types. Remaining differences in vehicle use patterns and driver demographics may account for some of the death rate differences.

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