A long combination vehicle is basically a very big truck. You know how some trucks only have one part, but others have a big part with a long part attached to it? Well, the long combination vehicle is like that but even longer! It's made up of two or more parts that are connected so that they can be driven together.
These trucks can be really, really long – sometimes up to 100 feet! That's like a whole school bus plus another car or two. Because they're so big, it takes special training and a special license to drive them.
They're mainly used for carrying a lot of heavy stuff like building materials or big machines. It's like having a moving house except it's a moving warehouse.
In many states, there are special rules for when and where these trucks can drive. They usually have to stick to certain roads or times when there's not a lot of traffic. That's because they take up so much space on the road and can be a little tricky to turn or stop. So, when you see a really big truck with more than one part, know that it's a long combination vehicle and is carrying a lot of important stuff, but also be careful around them on the road.