Current testing regulations only require light-duty vehicles of 8,500 lbs or less to be tested for fuel economy.

Engines for use in light-duty vehicles can be also emission tested using an engine dynamometer.

Today, automakers generally certify all their light-duty vehicles to meet standards in all 50 states because the separate regulations are not far apart.

The cost to convert a light-duty vehicle from gasoline to propane use ranges from $4,000 to $12,000.

The provisions apply to light-duty trucks and light-duty vehicles in California.

In the 2003 model year, the average light-duty vehicle weighed more than two tons for the first time since the mid 1970's.

Rebates of up to $5,000 per light-duty vehicle are available for individuals and business owners who purchase or lease new eligible vehicles.

That argument has carried weight in Europe, where about one-third of light-duty vehicles sold each year are powered by diesel engines.

The ratings indicate how likely a light-duty vehicle is to roll over during a single-vehicle crash.

It is somewhat smaller than the engine in the average light-duty vehicle.