Game mechanics are a tricky thing. The hardest part about designing a game is making the engine. The next hardest part is programming in the mechanics. A lot of times the mechanics can be difficult to implement for a myriad of reasons, ranging from hardware limitations to engine limitations. Well, one fun fact about Fallout 3 is that Bethesda's trains were powered by fast-moving NPCs.
Syfy Games spotted an article on PC Gamer, where a 4chan anon was tinkering around in Fallout 3 and asserts that the trains in the game operate via fast-moving NPCs.
Basically, the theory goes that instead of designing an actual series of functions to make the trains have physics in Fallout 3 they just put them on the heads of an NPC who ran really, really, really fast. It gives the illusion of speed.
In the game, it's impossible to tell that the train is actually being operated by an NPC. It looks like a train cart moving the way it should. In fact, if you check out the working subway mod from REZSoftwareMods you'll notice that the mod completely bypasses having players actually get on the train.
In the video you'll notice that entering the subway station and attempting to get on the train takes you to an instanced area featuring the inside of a subway. In reality it's just an enclosed map imitating a moving subway. When you “get off” it's just a loading screen to transition to the next map. It's all smoke and mirrors. And what if I told you... you were never on the subway?
Using these kind of methods for “transportation” have been done in games for a long time. That's not to mention that making actual subways players can ride on is very, very, difficult to do, because it needs a separate physics-state to be able to move while also carrying active entities. Very few companies actually have trains you can get on and get off of that work properly, just due to the difficulty of implementing the feature without it being a resource drain. Rockstar has been one of the few companies to manage adding trains and subways you can actually ride in GTA games.
However, in this case, Bethesda needed a few shortcuts for the sake of the Gamebryo Engine. A lot of people have complained about how poorly constructed it is. But at the end of the day, Bethesda managed to fool a lot of people into thinking the Fallout 3 subways were legit, and it helped them move tens of millions of copies of Skyrim. So who gets the last laugh at the end of the day?
I'm curious if we'll see similar tricks applied to Fallout 4 when the game releases this fall for home consoles and PC?