About 1980, I was visiting Cass, W. Va. and spent the day riding in the cab of the #3, the Mt. Emily Shay. This was in October and the temperature had dropped below freezing the day before. While we were sitting in Whittaker station for lunch, a crewman ran up to tell the engineer, "Red" McMillion, that a woman had slipped on ice at the restroom paviliion and broken her hip. An ambulance would be waiting at the Cass depot.
Once she was carried on board, Red headed down the mountain. It is normally a 45 minute trip to climb the four miles from the depot to Whittaker, including two swtichbacks. Red got us down in 15 minutes. I've never seen anyone reverse an engine so quickly at each switchback and the brakman had to really scramble to get back on board aftger throwing the switch. Shays can really accelerate, so while the average speed, point to point, works out to just about 15 mph, the maximum speed wouldn't have been much higher.
The first 1/4 of the trip was on a grade of 7%, dropping to 6% and then to 5% for the second half of the trip, with the final 1/4 mile from the tank to the depot on the level. Apart from the quick reversals in the swithcbacks, it was skill with the airbrakes that got us down the hill in record time. The #3 rode smooth and steady all the way.