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Is the Hyperloop the Greenest Track for Rapid Transit?

Sep 03, 2013

Credit: Elon Musk/Tesla Motors Credit: Elon Musk/Tesla Motors

Elon Musk, founder and CEO of SpaceX and Tesla Motors, last month released a preliminary design for the Hyperloop, a proposed solution for high-speed travel between cities. He explained in his design study that Hyperloop seeks to solve the chief problems with conventional travel, which tends to be either too slow, too expensive, or both.

One of our questions here at IMT Green & Clean Journal has to do with the expected environmental performance of Hyperloop. How might it compare with other modes of mass and rapid transit, or other proposed solutions? I posed that question to media relations contacts at Tesla Motors, but they did not respond. Nonetheless, it's possible to make some comments about Hyperloop's environmental implications, keeping in mind that the concept is preliminary. 

Musk has referred to the Hyperloop as "a cross between a Concorde and a railgun and an air hockey table." He writes that the system "consists of a low pressure tube with capsules that are transported at both low and high speeds throughout the length of the tube." The 28-passenger capsules ride on a cushion of air inside a steel tube and "are accelerated via a magnetic linear accelerator affixed at various stations on the low pressure tube with rotors contained in each capsule." His initial study plots Hyperloop's route between San Francisco and Los Angeles, its preliminary design, and the logistics of the system.

Credit: Elon Musk/Tesla Motors Credit: Elon Musk/Tesla Motors

Hyperloop employs clean technologies and some aspects of the design seem to offer energy savings and a relatively small environmental footprint. The transit line would be built mostly on the median of the I-5 highway, so little additional land is required. The steel tubes, two of them for two-way travel, are set on 20-foot concrete pylons placed every 100 feet. This elevated configuration avoids the environmental disruption involved with underground construction. Solar arrays cover the tops of the tubes to power the system. Individual capsules are powered by batteries.

Hyperloop reduces atmospheric drag on the capsules through streamlining and by maintaining reduced air pressure inside the tubes at 100 Pascals. This lowers drag force "by 1,000 times relative to sea level conditions ... equivalent to flying above 150,000 feet altitude."

I asked Eric A. Morris, assistant professor of city and regional planning at Clemson University in South Carolina, what he thought the environmental implications of the Hyperloop might be. Is it really "green"?

In a way, it's not exactly a fair question. Hyperloop is a preliminary concept and hasn't been extensively studied by anyone. Morris did tell me, though, that some of the key factors would be "how much energy it takes to move seats" and "how full those seats would be."

The chart shown here, taken from the Hyperloop document, suggests that energy consumption per passenger is potentially much lower than other modes, even rail. That's given the assumption of 70 percent occupancy, however, which may or may not pan out.

Credit: Elon Musk/Tesla Motors Credit: Elon Musk/Tesla Motors

One of the advertised benefits of mass transit is its lower environmental impact compared to automobiles. However, Morris has written that studies of energy efficiency in transportation are sometimes based on false assumptions -- for example, comparing the energy consumption of a car with one passenger to a transit vehicle with every seat occupied. "At any given time, the average auto has somewhere around 1.6 passengers, and the average (typically 40-seat) bus has only about 10," he said. Rail vehicles typically have more passengers, but rail cars are larger, so their percentage of occupied seats isn't that large on average, about 46 percent for heavy rail and 24 percent for light rail.

Credit: Elon Musk/Tesla Motors Credit: Elon Musk/Tesla Motors

The U.S. Dept. of Energy finds that automobiles consume 3,364 Btus per passenger-mile, whereas buses actually consume more, 4,240 Btus per passenger-mile. Rail is better, coming in at 2,462 Btus, but Morris points out that even that is not the kind of improvement you could refer to as a "slam-dunk advantage." Interestingly, the energy intensity of air travel compares well with other modes at 2,779 Btus.

"It is not clear that moving around large and largely empty vehicles is much of an improvement over moving around smaller ones," Morris said.

Morris does stress, though, that different modes of transportation run on different energy sources, and the environmental equations can change depending on those energy sources. Natural gas puts out lower levels of greenhouse gases (GHGs) than gasoline. An electric vehicle is almost pollution-free, but only if you disregard the energy source used to generate the power it runs on.

Credit: Elon Musk/Tesla Motors Credit: Elon Musk/Tesla Motors

Hyperloop's most obvious competitive travel solution is the California High Speed Rail system, scheduled for completion in 2029. The California High Speed Rail Authority says its system will run from San Francisco to the Los Angeles basin in under three hours at speeds of over 200 mph.

The authority projects that by 2040 the system will reduce vehicle travel in California by 10 million miles a day and will reduce flights by 97 to 180 per day. The system is planned to achieve net-zero energy operation and to run on 100-percent renewable energy from sun, wind, geothermal, and biofuel sources. The reduction in car traffic in the state will improve air quality, and the authority estimates its system will reduce GHGs by 5 to 10 million metric tons CO2 equivalent.

Musk writes that while "the underlying motive for a statewide mass transit system is a good one," he was "quite disappointed" when the California rail project was approved. The current projected cost is a whopping $68.4 billion. Average speed will be 164 mph, yielding travel time of 2 hours 38 minutes between San Francisco and L.A., compared to only 1 hour 15 minutes by air. The average one-way ticket price is now projected as $105, compared to round-trip air fare of $158 and the $115 cost of driving the round-trip by automobile. The planned rail system, Musk complains, "does not reduce current trip times or reduce costs relative to existing modes of transport." The Hyperloop study proposes a system that accomplishes both, with an energy cost lower than any current mode of transport.

Credit: Elon Musk/Tesla Motors Credit: Elon Musk/Tesla Motors

Musk says the Hyperloop's capacity would be "on average 840 passengers per hour which is more than sufficient to transport all of the 6 million passengers traveling between Los Angeles and San Francisco areas per year," even figuring that 70 percent of those passengers would be traveling during rush hour. In addition to the 28-passenger capsule, the design also envisions a capsule that can carry three vehicles. Musk estimates the cost of the Hyperloop at $6 billion for the passenger-only system and $7.5 billion for the passenger-plus-vehicle system. The trip between San Francisco and L.A. would take only 35 minutes and would cost an estimated $20 for a one-way ticket for the passenger-only version.

"Obviously this is a very new idea and needs more study," Morris said. And in his design document, Musk acknowledges that the Hyperloop concept has a long way to go. The design is released as "an open source transportation concept" specifically to spark new ideas that can be incorporated into future iterations. Given Musk's penchant for invention and entrepreneurship, it seems unlikely that he will just sit back and wait for others to improve on the Hyperloop design. In fact, he has mentioned recently that he will probably be building a demonstration prototype himself.