1) i don't think there is conclusive, clear and convincing proof that 2 pups can be unloaded faster than a van; Remember, by the time both pups are backed into the door, the van, which was backed in within 30 seconds of reaching the yard has already had 2 shipments or 4 pallets already unloaded. On top of that, i don't feel 2 pups can be unloaded faster than a van even if both were put in the door at the exact same time.
2) i'm not buying the single axle vs. tandem axle either for the following reasons.
a) End of line terminals that run niteliner usually don't have 2,3,4, niteliners, so not the majority of tractors and they don't have to share them with all the daytime P+D drivers; 3 or 4 tandem tractors vs. 20 single axle tractors.
b) The extra board city drivers or drivers that have more rural type routes with longer trailers could use those tandem tractors successfully.
So we're only talking a few tractors vs. the whole fleet of the terminal. Therefore the cost difference is negligible.
Sorry, but question STILL remains unanswered.