I used to work for a guy whose father or grandfather helped build the Mt. Washington railroad up in New England. It is a very steep railway with gear teeth in the center for the locomotive to grab on. The guys building it started at the bottom of the mountain going up to the top. At the end of the day they had to get down the hill. They used these 6-8' long flat cars with rail wheels. They would ride them down the mountain... and I don't think they had brakes. He claimed they hit 80 mph.