gravity!
they are invented so people can travel around easier
In Scotland we call that an "electric brae". There are one or two famous examples, which have become (in a small way) tourist attractions. It is a kind of optical illusion, where the lie of the land tricks your brain into thinking you are going downhill, when the physical reality is the opposite. There you go!
Whatever speed they're allowed by the driver of the vehicle.
The manufacture of cars in the Midwest opened up jobs. The cars and trucks made it so Farmers and other people could be connected to others better and they could haul stuff easier too. It relieved horses of being used for hauling people and things. Paved roads were created. Once heaters were put in cars the people could travel in warmth and travel farther. It also meant the doctors could get to their patients easier and faster.
They travel by plane, weird cars, weird buses... they travel with the same cars but weirder!!
cars were really fast, they had about 1000 horsepower and could go up to 300 mph. since the cars have went downhill, and have lost power, looks and style.
Solar cars have 4 wheels on the bottom that let them travel!
We need cars to travel about in
Going uphill, the vehicle engine is under stress while also being part of the weight holding the car back. In old cars pre-1970s, we often had to downshift into low to just maintain any amount of speed to get up a steep hill. Today's automatic engines do the auto shifting much easier than in older auto transmissions.
* they travel by cars and by boats
they travel in boats and cars
they travel with pie