Responses weren't surprising when the National Highway Traffic Safety Administration (NHTSA) announced on March 29 that it will toughen fuel economy requirements for SUVs, pickups, and vans. Vehicle manufacturers said it would be a challenge to meet the new requirements. Environmentalists said the agency should have done more.

The safety implications of the policy change are plain, though. The new requirements, which will phase in for 2008-10 models and take full effect with 2011 models, will remove the longstanding incentive for auto manufacturers to meet tougher fuel economy targets primarily by downsizing their vehicles, thus compromising crashworthiness.

NHTSA will continue to set fuel economy targets, but under the new system the targets won't be applied uniformly across a manufacturer's fleet of SUVs, pickups, and vans (the current uniform requirement for these vehicles is 22.2 miles per gallon). Nor will all manufacturers meet the same targets. Instead each fleet's fuel economy will depend on the sizes of vehicles sold. Bigger vehicles will have less stringent targets. This will remove the incentive to downsize vehicles and, in turn, greatly reduce the conflict with safety.

NHTSA won't set fuel economy targets quite the way it proposed last year. The proposal called for sorting SUVs, pickups, and vans into six categories with differing fuel economy targets (see Status Report, Feb. 25, 2006; on the web at iihs. org). The Institute responded by pointing out that this would give manufacturers room to 'game' the system by, for example, changing vehicle sizes and weights within categories without changing their fuel economy targets. This would mean safety could continue to be compromised because reducing vehicle size or weight reduces, on average, how well occupants are protected in crashes.

To discourage such maneuvering, the Institute suggested replacing NHTSA's proposed categories of vehicles with a continuous system under which each incremental decrease in vehicle size would trigger an incremental increase in the fuel economy requirement.

This is what NHTSA did, saying it agreed with the Institute about its "concern over the potential to downsize within a step function category, particularly the smallest size categories, where reducing vehicles' size or weight likely would have the largest impact on occupant safety."

This change in how fuel economy targets are applied represents the biggest departure from what NHTSA proposed in 2005. Another departure is a boost in miles-per-gallon targets, versus proposed ones, in part because of switching to a continuous system of assigning the targets. NHTSA also decided to subject some of the largest SUVs and vans to the new fuel economy requirements. These had been omitted in the proposal, and NHTSA says covering them will save fuel beyond the 9 billion gallons already projected from toughening the requirements for all SUVs, pickups, and vans.

In announcing the standards, U.S. Transportation Secretary Norman Y. Mineta said these are "the most ambitious fuel economy goals for light trucks ever developed." There's an important safety gain, too, because the standards finally unlink fuel economy goals from their consequences in terms of occupant protection.