Wentward with a little more stretch and a T950 Turbocharger. There was a mod on this https://www.worldofmods.com/beamng/cars/42156-wentward-dt45l.html
It was stolen without permission from this mod pack. It won't get any longer, but you'll get more out of it by getting the full pack. https://www.beamng.com/resources/wentward-pack.4628/ It's outdated, unfortunately, but it might still work. It's a very made mod.
Longer buses sadly are not compatible with a lot of bus stops in the game. If the devs ever add an longer or even bendy bus they will need to increase the length of the bus stops in bus routes mode first. Personally I would love to see more bus content in the game. Wentward feels quite old and a more modern bus would be interesting and fun. Buses also nowadays feature a lot of interesting power sources... from CNG to battery to fuel cell.
Oh my god, look how compact it is :O I think im inlove. Outdated could be 50/50 chance of proper function...what about the compact bus officially?