Problem: Current trains are crap. Even though many advancements to them have been made, there are still quite a few problems with them. Significant amounts of drag, friction, and pollution. Even without solving these issues, shipping on trains is much more economical than a truck due to lower friction and lack of stopping.
Lets break the problem down into parts:
Drag: It is the biggest opposing force on the train and causes it to be much less efficient than it's potential. Trains have been designed to have less drag but it is still the number one cause of wasted energy on the train.
Solution: Take the out the air. Though this sounds crazy, it can be done. We could have a tunnel that is a complete vacuum with a train running in it. If there's no air, then there's no drag. Simple
New problem: So we now have a train running though a vacuum. This creates another problem as well. Due to the nature of using ignited fuels, oxygen is required to make the train move. Don't worry. This problem will be soon solved.
Friction, fuel, and pollution: Friction of train wheels against a track is going to create friction, no matter how slight or minimal you can make it. This might not be as bad as drag but it is still a major problem to be noted. Since the beginning the steam engine, trains have been running on fuel that requires oxygen, as said before. We should fix this too. Pollution is a nasty problem too. Current trains burn diesel, which will release greenhouse gases into the atmosphere. They have the potential to make the earth warmer and create acid rain, which is bad for the plants.
Solution: Maglev. It does not require air in order to move. Since it floats above the track it has virtually no friction. The thing runs electromagnetically with electricity, which does not pollute. Isn't that great?
Maglev in a vacuum tunnel. This is going to change the world. With such a contraption, we could travel from Seattle to Beijing via a below-ocean tunnel in less than one hour! This means you can leave Seattle at 9PM and arrive in Beijing at 7AM. Since the only thing that the train has to overcome is gravity, once the train gets going at speed, it will take minimal energy to keep it propelled.
Soon, airplanes are going to be history.