NYC to LA in 21 Minutes: Inside RAND’s Wild 1970s Proposal for a 14,000-MPH Vacuum Train
The Very High Speed Transit System was an ambitious proposal by American scientist and engineer, Robert M. Salter.
Air travel has been the world’s main source of long-distance transportation for almost a century. Since its inception, air travel has helped the United States win wars, reshaped the transportation of goods, put satellites in space, and transformed the way we as a society travel. It is a miracle of modern engineering. However, back in the 1970s, an engineer named Robert M. Salter thought there was a better and more efficient way to get around. Forty years before Elon Musk ever uttered the word “Hyperloop,” Salter came up with a transportation idea that would have made air travel seem like a horse and buggy.
It was a high-speed train system called The Very High Speed Transit System—or VHST—that was theorized to be able to travel up to 14,000 mph. And, by Salter’s calculations, it would have been able to make the journey from New York to Los Angeles in just 21 minutes.
The VHST was born from “the search for a pollution-free transport method” that was likely the result of newfound climate data and the oil crises that plagued the ‘70s. But the unfortunate truth of most potentially revolutionary ideas like Salter’s is that they are both far too ambitious and too far ahead of their time to be realistic. However, the concepts in Salter’s proposal are detailed, fascinating, and thought-provoking, so who knows? Maybe this revisit will inspire someone to finally figure out a way to put a plan in motion.
A Man With a Proposal
The VHST was the brainchild of Robert M. Salter, an American scientist and engineer who specialized in particle and applied physics. He got his bachelor’s degree in mechanical engineering from Ohio State in 1941 and his master’s degree and a PhD in nuclear physics from UCLA in 1965. Throughout his career, he was involved with the Kettering missile program, the CORONA satellite project, and he even interned at General Motors for a bit while at Ohio State. But he spent the majority of his career at the RAND Corporation, where he helped come up with the idea for the first Earth-orbiting satellite. Later in his life, he set his sights on replacing air travel as the major source of long-distance transportation.
It might seem ungrateful to complain about air travel, especially back in the ‘70s. Just 100 years ago, cross-country travel would have taken days, if not weeks. Even in Salter’s time, plane travel meant you’d just take a nap, read a book, have a drink, take another nap, and you’d be there. Especially after the Airline Deregulation Act in 1978, which opened up airline travel to many more people. However, such incredible convenience came at a great cost and Salter knew it. Air travel is one of the most destructive forces to our atmosphere, and Salter understood that we were doing irreparable harm to our atmosphere at a time when climate scientists were already predicting an Ice Age.
One of the main reasons Salter came up with the idea for his VHST was to mitigate environmental damage. He pointed out that the energy spent in making an aircraft take off and fly to its destination is unrecoverable. It’s wasted energy. The process burns fuel and sends emissions into the atmosphere. And once the carbon dioxide genie is out of the bottle, there’s no getting it back in. But the proposed VHST would not only use very little energy getting up to speed, but it would actually recuperate energy while slowing down.
Thus far, there haven’t been any significant breakthroughs in alternative means of propulsion for large-scale planes other than fossil fuels. But what if, Salter proposed, we changed the method of transportation entirely? Salter’s idea would not only still allow people to travel across the country at speed and in luxury, but do so while producing little-to-no greenhouse gasses. All while being both significantly faster and more comfortable.
The resulting VHST was exactly what it sounded like—a very high-speed train system. The idea was to have one long, underground tunnel that would eventually stretch from New York to Los Angeles, with only a couple of brief stops along the way. Inside, the tunnel would have the majority of its air evacuated, creating a vactrain with the equivalent atmospheric pressure of 170,000 feet of altitude. The train would be magnetically levitated which, according to Salter’s proposal, would allow it to theoretically reach speeds of up to 14,000 mph.
That isn’t a typo. I didn’t add too many zeroes. Fourteen. Thousand. Miles. Per. Hour. For reference, the fastest commercial plane in history was the Concorde, which was able to reach 1,354 mph. Salter’s train idea would have been 10 times faster.
As mind-boggling as that sounds, Salter claimed it was technically possible. Not only that, but he also claimed that it wouldn’t even require the development of new technology. In 1972!
How the VHST Was Proposed To Work
It was all about removing resistance from the equation. In an evacuated tunnel, there’s little to no air resistance, which means the train could theoretically reach unbelievable speeds with relatively little energy. Maglev is a big part of the reason, too. Not only are maglev trains fast but they don't generate friction, which means there’s even less resistance and even higher speeds can be achieved with less energy. Stick a maglev train in an evacuated tunnel and you double your slipperiness, which is what would allow for the extraordinarily high speeds Salter proposed.
You can read the proposal in full below.
The maglev train would be driven via a loop of superconducting cable that, according to the proposal, would carry a million amperes of current. Achieving superconduction, of course, would require cooling the magnets down to less than minus 450 degrees Fahrenheit, and the cryogenic fluids Salter suggested for the job wouldn’t be “actively refrigerated underway” but instead replaced at terminal points, per the proposal. The “boil-off” would be stored over the course of the route and recycled during the “turnaround” process. The proposal is not clear on where the energy to supercool the magnets would come from.
That absurd-sounding 14,000-mph top speed would only happen briefly, however. The train would initially accelerate at around 0.5 Gs, reach its maximum speed for just a few moments, and then begin slowing down. Even then, Salter predicted a New York to Los Angeles trip—a distance of 2,451 miles as the crow flies—in 21 minutes. Although, that was a nonstop case. To make the VHST more practical, Salter proposed having two stops along the way in Chicago, Illinois, and Amarillo, Texas, to allow passengers to make connector trains to other parts of the country. With two stops, the total cross-country time would have increased to 37 minutes.
Obviously, such an idea was out of this world ambitious, but Salter’s proposal was patient. At first, the tunnel would only travel a few hundred miles, from New York to Chicago, for example. It would also have branching tunnels that would take additional trains to several different parts of the country. Eventually, the main tunnel construction would reach LA after many years of continuous development.
Imagine that, though. Just imagine going in the subway in New York, getting on a train, and being in California in just over 20 minutes. It doesn’t seem humanly possible.
Revolutionizing Mass Transit Forever
It was estimated at the time that the VHST would only cost $1 in electricity per day. With additional operating costs, Salter proposed a fare cost of $50 ($300 in today’s money) per person, which is considered a normal flight cost by present-day standards. So despite the enormity of the project, it wouldn’t have even been all that expensive for passengers to use.
But it wasn’t just the environment Salter wanted to improve. He emphasized quality of life elements as well. Planes are incredibly loud, airports take up vast swaths of land, and traffic surrounding airports causes immense congestion. Creating a subterranean method of high-speed travel eliminates many of those issues. He also wasn’t a fan of supersonic transportation—such as the famous supersonic passenger jet, the Concorde—due to their sonic booms and filthy emissions.
There were also benefits that went beyond personal transportation. Salter suggested tying other underground utilities to the VHST via adjacent tunnels, thus eliminating the need for additional tunnels. Oil, gas, water, and waste tunnels could all be run alongside the VHST tunnels, which would not only make digging the tunnel more cost-effective, but would also reduce overall maintenance labor and costs. He also proposed creating neighboring freight train tunnels for hauling cargo containers and heavy equipment. Those freight trains wouldn’t travel as quickly as the VHST but would still reach their destinations significantly faster than they do now.
Technically Possible But Unbelievably Difficult
While Salter claimed his VHST was technically possible, that’s like saying a real Iron Man suit is also technically possible. With unlimited funding and resources, an infinite timeframe, and state and federal governments always willing to play ball, sure, such a vactrain was technically possible. However, the challenges were immense. Salter had answers to every problem but none of them were easy and all of them were out of reach, which meant that VHST was probably never going to happen. At least back then.
Lateral acceleration was one of the biggest hurdles. Sideways forces through subtle bends would have to be kept down to one G or less for safety. To keep lateral acceleration under one G through a bend at 550 mph, the radius of the bend would have to be at least four miles. At 5,500 mph, the radius of a bend couldn’t be smaller than 400 miles. Remember, Salter wanted this train to reach a top speed of 14,000 mph, so you can imagine how arrow-straight the tunnel would have to be.
In order to safely maintain such high speeds, there would also need to be checkpoints set up throughout the tunnels. Each checkpoint would require the train to meet certain parameters such as speed, thrust angle, and thrust force. That way, if the train ever failed to meet certain required parameters at any given checkpoint, it could be shut down for safety.
That’s one of the reasons why Salter proposed an underground tunnel, as it would be next to impossible to create an above-ground tunnel that could cross over existing terrain and infrastructure without having to make smaller-radius turns. While it might already seem next to impossible to tunnel from one end of the country to the other in a near-perfect line, Salter felt that it was still easier to do that than to run the train above ground. He did admit that the cost of tunneling thousands of miles would be greater than building an above-ground train but he estimated that the benefits outweighed the initial tunneling costs. Even the International Advisory Conference for Tunneling agreed and said that tunneling would alleviate “a wide range of problems related to urbanization,” according to Salter’s proposal.
There was also the question of actually evacuating the tunnel of air. To create a perfectly vacuum-sealed tunnel that large, Salter said the tunnel would require expensive diffusion pumps or ion pumps, and a lot of them. Not only would that have been incredibly expensive, but it would also have drawn a ton of power. Remember, Salter was very conscious of the energy-efficient nature of this idea.
So instead of using such pumps to create a perfect vacuum, Salter felt that vacuum roughing pumps throughout the tunnel would do the trick. While they wouldn’t provide the perfect vactrain, they would drastically reduce the air resistance in the tunnel, bringing it down to about 0.5 mmHg, which is the equivalent of 170,000 feet of elevation.
Salter felt that if the train’s body would have been streamlined enough, it would cut through the low atmospheric pressure without overheating. Although, the only place said to heat up would be the nose, which would have been protected by a heat shield.
To create that level of atmosphere in the tunnel, Salter estimated that it would require $78 million in pumps (or about $550 million in today's money). He recommended 2,600 pairs of CFM pumps per mile at a total of around 5,000 miles.
However, according to Salter, the largest obstacles to clear were political ones. “It should be cited that the political outlook is much less optimistic than the technical one,” he said in his proposal. Getting state and federal governments to permit tunneling across the nation proved to be incredibly difficult. And that’s before you factor in air transport and oil lobbyists, who would have surely fought tooth and nail to stop Salter’s VHST if it ever got beyond the proposal stage.
Maybe the VHST Was Just Too Ahead of Its Time
Salter understood the technical and political challenges better than anyone, but he was adamant that the VHST not only needed to be built at some point, and that it was absolutely doable.
“Are there compelling reasons for the VHST to be built? The answer to this is an emphatic yes!!” Salter wrote. “We can no longer afford to continue to pollute our skies with heat, chemicals, and noise, nor to carve up our wilderness areas and arable land for new surface routes.”
Maybe he was willfully naive to the difficulties of a VHST and how anti-train much of our political landscape continues to be, being that it’s been more than 40 years and the U.S. still has no such high-speed rail system. However, Salter was neither the first nor the last to propose the idea. His was just the most ambitious.
Vactrain proposals date back to 1799 when British engineer George Medhurt proposed his Atmospheric Railway: a steam train inside of a partially evacuated tunnel. More recently and most famously, Elon Musk proposed the Hyperloop, which would use low-pressure tubes. And yet, despite Musk’s engineering resources and modern technology, there’s still no Hyperloop. Nor is there an Atmospheric Railway or a Very High Speed Transit.
Thankfully, it seems Salter’s optimism for a new method of high-speed transportation isn’t dead. Richard Branson’s Virgin Hyperloop recently completed its first passenger test in an above-ground tunnel with an interior air pressure of 100 Pa (the equivalent of 200,000 feet elevation). However, the tunnel was only 500 meters long and the passenger pod only hit a top speed of 107.5 mph. It’s very far off from Salter’s and even Musk’s goals, but it’s a start. Another company called HyperloopTT is also working on an above-ground evacuated train, with top speeds of 500 mph, similar to a commercial jetliner.
As impossible as such ideas may seem, a high-speed train should never be out of our sight. We should always be on the lookout for faster, more convenient, and more efficient means of long-distance mass transportation for all. Salter died in 2011 and his idea for a VHST never came to be, nor has anyone else’s yet.
But that doesn’t mean we should stop trying.
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