How vactrains work

In the middle of 1800s, the United States built the transcontinental railroad to get people and products across the country. By today's standards it was a slow way to go — about 8 days to get from Omaha to San Francisco.

At the time, however, the transcontinental railroad was a technological marvel. The same trip in a covered wagon took six months if things went well. When they didn't go well, it often meant death. Compared to a dangerous six month journey, eight days in a train seemed like light speed.

In the middle of the 1900s, trains were replaced by jet airplanes. Now a person could fly from New York to Los Angeles in six hours, at 550 miles per hour. At the time this too seemed like a technological marvel. But here we are 50 years later, and nothing has really changed. The obvious question is: What's next?

One possibility is supersonic travel. Supersonic airplanes currently cannot fly over land in the United States because of the sonic booms that they create. But new technologies could soon give us supersonic planes that do not have sonic booms. However, supersonic planes are not really the answer. First, they will be limited in their speed to 1,000 to 1,500 mph. While that is much faster than today's jets, it is not revolutionary.

The second problem is the cost per passenger. As the speed of a plane increases, so does the amount of fuel required to overcome air resistance. When the supersonic Concorde jet was flying, it took six times more fuel per passenger to get through the air. Thus the Concorde was too expensive for most people to afford.

The ultimate solution is likely to be a vactrain, also known as Evacuated Tube Transport or ETT. In a vactrain system, a magnetically levitated train moves through a vacuum sealed tube. The vacuum means no air resistance, and the magnetic levitation means no resistance from wheels or tires. Removing these two sources of drag creates two huge benefits. First it means that the train can go incredibly fast — with a top speed of 5,000 miles per hour. Second it means that the amount of energy required to move the train is very small. There are new energy costs to maintain the vacuum and to cool and power the magnets, but these energy costs are minimal compared to a jet.

The bottom line is that a vactrain between New York and Los Angeles would allow people to commute from one city to the other if they wanted to. The travel time would be less than an hour, and the price of a ticket would be low.

The only real constraints on a vactrain system are: 1) the need to place the tube, and 2) the need to keep the track straight. At 5,000 miles per hour, only the gentlest of turns are possible or passengers would feel the G-forces. A left turn, for example, might cover several big states. On land, a vactrain system could be put underground in tunnels, or it could go in steel or concrete tubes above ground. To cross an ocean, the tube might be anchored with cables on the ocean floor, with the tunnels floating mid-ocean.

The idea of a vactrain system that crosses the United States is exciting. But the global picture is even more interesting. With a vactrain system circling the planet, it is easy to imagine travel from the U.S. to China taking only 2 hours. New York to London might take only an hour or so. The system could carry both passengers and cargo, so shipping times and costs could be drastically reduced.

A vactrain system circling the globe might sound far-fetched today, in the same way that transcontinental jets would have sounded far-fetched in 1900. But there is already research under way in China to bring an early version of a vactrain to market. This first system would have only a partial vacuum, but would allow trains to travel up to 600 mph. China already has hundreds of miles of high speed rail traveling at 200 mph, and a vactrain would lower travel times significantly.

— — —

Marshall Brain, founder of HowStuffWorks, at marshall.brain@howstuffworks.com.