New York City Mayor Michael Bloomberg says “fuel-efficient” heavy trucks should get a discount if the city starts charging fees to vehicles that enter Manhattan during the day.

The Associated Press reports the mayor defines “fuel-efficient” heavy trucks as those with 2007 model-year engines, and that he is proposing that they pay only $7 instead of the $21 other trucks would pay.

He recommends that cars be charged $8 to enter central or lower Manhattan.

Bloomberg is proposing the fees as a way to cut down on congestion and pollution.