Faster than a bird, a plane, and a high-speed train, riders in a conceptual hyperloop pod could cover the 400 miles from San Francisco to Los Angeles in about half an hour. Yet for all the time-saving promise of hyperloop, there remain questions about passenger comfort, system costs, land use, and safety.

Hyperloop is a concept for a new very high-speed intercity transportation mode that would look something like this: A sealed, fixed tube partially evacuated of air encloses capsule-like vehicles zooming by at up to 750 miles per hour and drawing power from solar panels.

A recent Volpe report on behalf of NASA explores the feasibility of the hyperloop concept.

“Air travel, high-speed rail, and maglev have all been tested in the real world, to varying degrees,” said Volpe economist Catherine Taylor, the report’s lead author. “Here we take a deep, objective look at what we know and don’t know about the many major research questions still on the table regarding hyperloop.”

Open Questions About Hyperloop for Passengers and Freight

When transportation entrepreneur Elon Musk first presented the hyperloop concept in his 2013 white paper, he assumed hyperloop would be subject to similar security measures as those at U.S. airports. However, the Volpe team notes that as a fixed guideway system, the security process for hyperloop could be similar to that used for rail, which is much less time consuming than for air travel.

If hyperloop used stations built at the outskirts of cities, the time savings of hyperloop compared to rail—which tends to have stations in downtown areas—may be eroded. Compared to automobile travel, potential time savings of hyperloop travel at shorter distances may be eaten up by check-in procedures and passengers having to access terminals outside of city centers.

At longer distances, cost savings compared to air travel may be eroded due to right-of-way acquisition and construction costs.

“For passenger travel, about 900 miles has been mentioned as the maximum range for hyperloop,” said Taylor. “But it may be more realistic to focus on markets that are 250 to 500 miles apart.”

In high-speed hyperloop travel, speeds could reach up to 750 mph. (melpomen/123RF photo)

Passenger comfort is another area the Volpe authors explored.

At very high speeds, hills and curves exert g-forces on passengers. A 1994 Volpe study explored human comfort thresholds related to g-forces, and a presentation from Hyperloop Technologies—now Hyperloop One—cited similar tolerances as those found in the Volpe study, indicating the industry is aware of passenger comfort issues.

Recently, hyperloop firms have focused on proving the technology for cargo travel. Conceptual renderings show a freight pod large enough to accommodate a standard shipping container, but there has been no discussion on tonnage limits for freight pods.

A conceptual rendering of a freight pod large enough to accommodate a standard shipping container.

“The most compelling feature of the hyperloop concept may be the potential for it to provide service underwater,” said Taylor. “The combination of air, truck, and rail service offerings provides a wide spectrum of cost and speed trade-offs for freight movements over land. For shipments over water, there is only air, which is fast but expensive, and ship, which is slow but cheap. There may indeed be a need for an additional mode for sea shipping.”

System Costs

Early estimates of $17 million per mile for a passenger-only hyperloop system from San Francisco to Los Angeles are less than one-tenth the cost of the California High Speed Rail project covering the same route. Later estimates pin the general price of hyperloop at up to $27 million per mile, not including land acquisition costs, conceptual engineering, final design, and environmental planning—all of which could significantly drive up construction costs.

Costs to operate and maintain a hyperloop system are missing from available sources, but are needed to gain a comprehensive understanding of the total price tag for a hyperloop route.

Land Use and Safety Issues

In the transportation research world and in the public consciousness, hyperloop is often thought of as a long-distance travel solution. But its network of fixed tubes needs access to rights-of-way, and that access is often controlled by state and local governments.

“It’s an open question as to whether localities would want to give up resources they could use for their own transit needs to serve a long-distance travel mode,” Taylor said.

In addition, fire and police departments are likely unable today to handle emergencies in this new transportation mode. Hyperloop routes would pass through rural areas where local emergency departments may not have specialized equipment and expertise to evacuate an elevated hyperloop system following a passenger emergency, system malfunction, or power outage.

“It’s not all faster, cheaper, smarter, better,” Taylor said. “Like every new technology, hyperloop has pros and cons, coupled with a great deal of uncertainty on how much it will cost.”

Seven Key Questions

The Volpe authors conclude their report with seven questions to spur further thinking and research on hyperloop feasibility:

1. Is the hyperloop transportation system sufficiently lightweight that there would be significant construction cost savings compared to building an elevated high-speed rail or maglev system?
2. What are the technology hurdles to building hyperloop underwater and can they be overcome?
3. Can the capacity of a hyperloop pod be expanded to seat more than the originally proposed 28 passengers?
4. What would be the weight limit for a freight capsule?
5. How big would the tube need to be in order to carry a standard size shipping container?
6. Can the system be designed so that in addition to carrying long distance passengers, it can also provide local transit service?
7. Would hyperloop be loud for passengers? Would hyperloop be loud in communities?

Taylor presented the results of this report at the 2017 AIAA SciTech Forum in Grapevine, Texas, on January 9 in a session chaired by representatives from NASA and Hyperloop One.

Read the full report, Hyperloop Commercial Feasibility Analysis, by Catherine Taylor, David Hyde, and Lawrence Barr.