Skip to 13:15 if you just want to see the cars. A lot of the tracks don’t have the computer trained on them, so you can’t play them single player other than doing time trials. And some of them just crash. But the ones that do work are pretty cool though.
From Wikipedia :
Less than a year after publishing POD, Ubisoft issued an expansion pack under the title Back to Hell (also known as Extended Time in France) in late 1997. This pack contained 19 circuits and 15 new vehicles, including motorcycles, a floating purple batlike creature, and a witch riding a broom.