Oh good grief! I think we've all forgotten about "18 Wheels and a Dozen Roses" by Kathy Mattea. What a sweet little song -- just made for Dobro and mandolin -- and all those natural harmonies.
Also -- on the novelty side -- "There Wouldn't Be No Truck Drivers if it wasn't for us Trucks." Recorded by Dave Dudley, I think.
Finally, though it's on the edge, "Me and Bobby NcGee." "... We sang every song that driver knew ..." etc etc.