Dump truck driving is nearly always local. Meaning it's lower paid, typically smaller companies, fewer requirements, easier license to get. A lot of dump truck drivers own their own trucks. Cement trucks are similar except that the drivers are normally employees rather than owners.
Employee dump truck drivers are seldom paid by the load, at least around here. But that doesn't mean they don't drive too fast- people do that in cars and on bicycles, too, you know. People will speed up to get to a red light sooner, after all.