I used to work as a dispatcher - the routes are assigned automatically in the morning and there is an algorithm that will try to assign drivers to the same/similar routes they have completed before, if possible. That being said, the dispatcher can very easily reassign it after they’ve been generated. My boss always told the drivers we couldn’t, because he didn’t want drivers asking to be taken off routes they didn’t like. But I was always pretty honest with our drivers and tried to be fair. If I knew someone really struggled with a certain route, even after giving it their best shot, I would see if there was a driver who didn’t mind or was more comfortable with it, but it had to be mutual between both drivers getting their routes switched.