The train was pulled by a steam locomotive. Very cool, still in use in parts of Europe. Steam locomotives generate steam via a boiler which is heated by someone shoveling coal into a firebox. They made a point of showing the fireman feeding the coal into the firebox so the train can go. They made a point of showing how the bad guys got rid of the engine crew, therefore no one was feeding the fire anymore. Yet the train scene went on for like half an hour (maybe only 15-20 minutes, but damn, it went on a long time) and the engine would've been out of fuel in minutes. Oh no! The train is speeding out of control! There's no one to apply the brakes! Yeah, there's no one feeding the fire, either, so the train should've stopped a long time ago. By the end of it, I was laughing so hard I couldn't breathe because that damned scene kept going on and on and on, crash, smash, boom, creak, crash, boom, creak, creak, crash... What a fucking scene! So exciting! And didn't make a goddamned bit a sense. Oh, that's right; it's a Mission: Impossible movie.
The thing is, I can buy that Ethan Hunt is practically superhuman and can climb, run, do card tricks, whatever. I can even buy that he can jump off of a moving vehicle and grab something and land on his feet and whatever other silly shit is going on. But how in the hell is a steam locomotive still pulling a train at 100 miles an hour through the fucking mountains when it ran out of fuel half an hour ago and you even made a point of showing that that's the case?