Its the worst. You're constantly sandwiched between employers who expect you to be on the road for a full 13 hours, and police who will slap you with huge fines or take your license if you work over those 13 hours.
Every slow car in front of you or delay at a depot compounds into a stress that eats away at you. Which side is going to win out today? Are the cops going to take my license, or is the company going to sack me for not making my delivery on time?