I actually delivered for Dominos in those days. The 30 minute guarantee was not the reason drivers were dangerous. Stores had a limited delivery area that was set up so that you could get anywhere in about 10 minutes at normal traffic speeds. Drivers were not punished for late deliveries; in most cases when that happened, you and the manger both knew it was going to be late before it left the store.
The reason some drivers were reckless is because there was a commission on each delivery (and you often got tips as well). The more you delivered, the more money you made. In reality it didn't amount to much because you can't really drive much faster than the prevailing average traffic, you burned more fuel and wore out your brakes and tires if you drove like an idiot, but some drivers did anyway. It was heavily discouraged by the managers, at least where I worked.
