The Department of Transportation is a big group of people who work together to make sure that transportation (moving around from place to place) is safe and easy for everyone.
Imagine you want to go on a vacation to the beach with your family. You need to drive there, right? The Department of Transportation is responsible for making sure that the roads you drive on are well-maintained and that there are clear signs telling you where to go. They also make sure that the bridges you cross are sturdy and safe, so you don't fall in the water!
But the Department doesn't just take care of cars and trucks. They also make sure that planes, trains, and buses are safe for people to ride in. They inspect planes to make sure they are working properly and have good pilots, they make sure trains and buses run on time and don't crash into each other, and they keep all the roads and tracks clear of snow and ice so you can still get around in the winter.
Overall, the Department of Transportation is like a big group of grown-ups who work really hard to make sure you can go where you want to go safely and easily, no matter how you're getting there!