Some vehicles can't be driven by companions. Right now, it's a bit basic for ease of implementation, but it'll be further elaborated upon later.
A companion can be told to drive your last driven vehicle (or stop driving) via dialogue.
Pioneer, MoreArmor, and Car Caller add-ons fully integrated some mesh work on van, highway patrol car, Pioneer, and deathcar interiors
Updated TTW patch by Xorpie now available at the following link: