This would allow trucks to be averaged separately so their lower mileage doesn't drag down the average for cars. This in and of itself may not be such a bad thing. The problem is that automakers have abused this split over the years to make their mileage look better than it has been. Companies have taken vehicles that were obviously passenger cars and tweaked them to get classed as light trucks so they pull up the average of the big SUVs. A prime example of this is the Chrysler PT Cruiser which gets lumped in with the Dodge Ram. If the rules could get written such that these types of shenanigans are prevented, the car/truck split would be OK. Levin also wants to stretch out the time-line for implementing the new rules and restore the separate fleet averages for import and domestic vehicles.
[Source: Detroit News]