When my lottery numbers finally come-up and I start assembling the dev team for Total Transport Simulator (a combo plane/train/automobile/ship sim) Pierre-Michel Ricordel is going to be the first person I call.
He's the bloke responsible for extraordinary freeware truck sim Rigs of Rods. Imagine a hybrid of 18 Wheels of Steel, Bridge Construction Set, and Garry's Mod, and you'll probably just strain your brain. Far better to download the thing, together with a few choice add-ons, and experience the amazing vehicular physics first-hand.
Don't quit before you've driven a Tatra lorry into the belly of an Antonov cargo plane then taken off, messed around with at least three types of truck-mounted crane, and tried a spot of rock climbing in one of the big-booted, insanely flexible, crawlers.