Double-stack car

Okay, imagine you have a toy train set. Normally, you can only put one train car on top of another one if they are flat and the same height, right? But sometimes, grown-up trains use a special kind of car called a double-stack car.

A double-stack car is like a bunk bed for toy train cars. Instead of having just one flat deck for a train car to sit on, it has two decks! This means you can put one train car on the bottom deck and another one on top of it, like a bunk bed.

But how do the trains stay in place without falling off as the train moves? Well, the double-stack car has special walls that come up around each train car to keep them from sliding around. And the top train car has a special cover called a "tunnel" that keeps it safe from things like tree branches or tunnels that the train might have to go through.

Why do grown-up trains use double-stack cars? Well, for one thing, it lets them carry more stuff without needing more train cars. They can fit two layers of shipping containers or trailers on one double-stack car instead of just one layer. This means they can transport more goods at one time, which is better for the environment and also saves money.

So, that's what a double-stack car is - it's like a bunk bed for trains that lets them carry more stuff!