Well, unless it is a government load, the fuel "subsidy" going to the truck is not from the government. It is from either the shipper or the receiver. Government only pays a fuel surcharge on their own loads. And that is what it really is called... a fuel surcharge. It is calculated differently by different folks and the formula calculation is agreed to by both parties. Government does not pay fuel surcharge on private entity interstate commerce.
But on a side note, diesel has come down in price right along with gasoline. Just not for the general consumer. I have filled the truck all this last week at a cost of $1.83 a gallon for diesel. I get a discount off the cash pump price, so basically paying the rack invoice price for fuel. La Salle, IL for instance, the cash price right now as I write this is $2.90 a gallon for diesel. I get $1.07 a gallon discount, for a actual cost of $1.83 a gallon. I average 7 mpg with the truck. Fuel surcharge to the truck is 35 cents a mile right now. So, for every gallon of fuel I use at $1.83 a gallon, I get a fuel surcharge of $2.45. So, essentially, instead of my fuel costing me, I actually net 62 cents a gallon.