That is your DM local policy. He can do anything he wants.
But, according to the law, if they work over 14, they just need 10 hours off to drive again. But most of the drivers being used as helpers are on Friday or Saturday because they have reached their 60 hours already.
You need 34 hours off to reset your 60.
No, they just need 10 hours off to drive again. Unless they already have their 60 for the week.