There is a max length and tonnage rule for van trains, but not for freight. The vans can't exceed 10,000 feet or 9,000 tons and that rule is followed to the letter.
Freights are more go with what is known to work. The 70 ACe's and MAC's are known to pull well so they will go with two of them on an 8,500 ton train. The GE 6,000 HP engines will pull to, and faster as long as the rail is dry. They are slippery when the rail is wet.
There is a reason why you almost never see a set of the new ES4400DC's heading a heavy freight on the B&A. They don't work well on the B&A in that service.
Last year, they were trying to pull 10,000 tons with the new 700 series ES4400AC's, and it did'nt work out to well. Lots of stalled trains.
