There are many similarities between Trains and Cars. Both are large and primarily made of metal; both have engines; both have drivers; both are means of transportation. Even the individual units of a train may be referred to as "cars". But you must remember that your car is really an automobile, not part of a train.
Stringing two automobiles together does not make a train, it is called "giving a tow." The engine of a train is an entire separate car, the engine of car is inside the car, and probably right in front of you. In a car the driver could be you, on a train the driver is definitely not you.
This means that you can take a snooze in your bed, have sex, have a smoke between cars, pace back and forth, write a novel, recite the entirety of Yevgenii Onegin, do gymnastics, eat an entire chicken, etc all along the way.
It also means that you can't stop at the little Ma&Pop joint, take a picture with the giant plaster cow, or suddenly decide to swing by Texas before you get to Gran's in Utah.
Trains are intended for mass transport of goods or people. They have fixed routes and schedules, and you may hitch a ride for part of the route, but the train keeps going even after you get off. A train has its own agenda.
Highways are intended for mass transport of people or goods. They have fixed routes, and you may hitch a ride for part of the route, but the highway keeps going even after you get off. A highway has its own agenda. But a highway is also not a train.
A highway is not made of metal, a highway has no engine, no driver; highways do not "give a tow."
If you step in front of an automobile, it probably won't hit you. If you step in front of a train, it probably will. You can't step in front of a highway.
A train is attached to its highway. Automobiles travel along highways, but they are not attached to them and they are not intended for mass transport of anything. They are intended for individual transport and you must have your own agenda.