TDM also makes semis (lorries to you Brits) which although would be really neat, it's definitely not practical to have in EvoCity and 2 are probably more difficult to control than even a bus or firetruck atm. So people will end up crashing into every car they see, or refusing to stop in time plowing through cars claiming they couldn't brake or they lagged.
While I would love to add these also, refer to my previous comments about content size being a problem for new comers.