WASHINGTON President Bush signed energy legislation last month that, among other things, sets the government on a course to start regulating the fuel efficiency for large commercial vehicles, including over-the-road buses.

It also mandates an expanded role for biofuels, requiring that the level of biofuel/standard petroleum blends be on an annual schedule.

Most of the media focus on the energy bill centered on the higher fuel economy standards for automobiles and light trucks, which were raised for the first time in 32 years.

But the bill also has important long-term implications for operators and manufacturers of commercial vehicles and their engines.

At one point, the House version of the bill contained a provision that would have required medium- and heavy-duty commercial vehicles to show a 4 percent annual improvement in fuel economy starting in 2016, based on the average of city and highway miles for each class of vehicle in 2013.

After a vigorous lobbying effort by engine manufacturers and others, that provision was spiked in favor of a plan to figure out how to measure commercial vehicle fuel economy, and then put standards in place.

Specifically, the law gives the National Academy of Sciences one year to study the issue, taking existent and potential technologies into account.

When the study is done, the U.S. Energy and Transportation Departments and the Environmental Protection Agency will have two years to start writing a rule to set and enforce fuel efficiency standards for commercial vehicles.

The agencies will have to set test procedures as well as the appropriate metric for measuring fuel economy, taking into account the work the vehicle is doing and the operational conditions. At a minimum, the regulators will have to give vehicle and engine manufacturers four model years of lead time to meet the standards, and three model years of stability.

The law also sets a schedule for annual increases in renewable fuels, including biomass-based diesel. And it calls for studies of the effect of biodiesel on engines and the adequacy of the biodiesel transport system.

Officials at all levels of government are beginning to worry about the thousands of over-the-road trucks that will be needed to transport the raw materials for biofuel plants, as well as the finished fuel. Pipelines for such plants do not exist and are not likely to be built given the relatively small scale of most biofuel plants compared to giant petroleum refineries.