Four years ago, I broke my comment section by declaring that Elon Musk’s Hyperloop proposal had no merit, combining technical criticism with expressions like “barf ride” and “loopy.” Since then, Musk seems to have quietly abandoned Hyperloop, while the companies attempting to build the technology, run by more serious people, are doing away with the promise of reducing construction costs to one tenth those of conventional high-speed rail. Instead, Musk has moved to a new shiny target in his quest to sell cars and compete with public transit: The Boring Company. I criticized some of what he was saying in Urbanize.LA last summer, but I’d like to go into more detail here, in light of a new fawning interview in Wired and an ensuing Twitter flamewar with Jarrett Walker. In short, Musk,
a) has little understanding of the drivers of tunneling costs,
b) promises reducing tunneling costs by a factor of 10, a feat that he himself has no chance to achieve, and
c) is unaware that the cost reduction he promises, relative to American construction costs, has already been achieved in a number of countries.
The Boring Company’s Ideas of How to Cut Costs
There is much less technical information available publicly than there was for Hyperloop. However, The Boring Company has an FAQ including an outline of how it aims to cut construction costs:
First, reduce the tunnel diameter. The current standard for a one-lane tunnel is approximately 28 feet. By placing vehicles on a stabilized electric skate, the diameter can be reduced to less than 14 feet. Reducing the diameter in half reduces tunneling costs by 3-4 times. Second, increase the speed of the Tunnel Boring Machine (TBM). TBMs are super slow. A snail is effectively 14 times faster than a soft-soil TBM. Our goal is to defeat the snail in a race. Ways to increase TBM speed:
- Increase TBM power. The machine’s power output can be tripled (while coupled with the appropriate upgrades in cooling systems).
- Continuously tunnel. When building a tunnel, current soft-soil machines tunnel for 50% of the time and erect tunnel support structures the other 50%. This is inefficient. Existing technology can be modified to support continuous tunneling activity.
- Automate the TBM. While smaller diameter tunneling machines are automated, larger ones currently require multiple human operators. By automating the larger TBMs, both safety and efficiency are increased.
- Go electric. Current tunnel operations often include diesel locomotives. These can be replaced by electric vehicles.
- Tunneling R&D. In the United States, there is virtually no investment in tunneling Research and Development (and in many other forms of construction). Thus, the construction industry is one of the only sectors in our economy that has not improved its productivity in the last 50 years.
This is not the first time that Musk thinks he can save a lot of money by reducing tunnel diameter; he said the same thing in the Hyperloop paper. Unfortunately for him, there is literature on the subject, which directly contradicts what he says. In my Urbanize piece, I mention a study done for the Very Large Hadron Collider, which compares different tunnel diameters across various soil types, on PDF-p. 5. Two tunnel diameters are compared, 4.9 m (16′) and 3.9 (12′). Depending on soil type and tunnel boring machine (TBM) drive, the larger tunnel, with 1/3 larger diameter, costs 15-32% more.
Subsequent pages in the study break down the costs per item. The TBM itself has a cost that scales with cross-sectional area, but is only a small minority of the overall cost. The study assumes five drives per TBM, with the first drive accounting for 75% of the TBM’s capital cost; in the first drive the larger-diameter tunnel is 32% more expensive, since the TBM accounts for 25-40% of total cost depending on diameter and rock, but in subsequent drives the TBM accounts for about 5% of total cost. Another 6% is muck cars (item 2.05, PDF-pp. 7 and 46), whose cost rises less than linearly in tunnel diameter. The rest is dominated by labor and materials that are insensitive to tunnel width, such as interior lighting and cables.
But the actual cost is even less sensitive to tunnel width. The VLHC study only looks at the cost of tunneling itself. In addition, there must be substantial engineering. This is especially true in the places where transportation tunnels are most likely to arise: mountain crossings (for intercity rail), and urban areas (for urban rail and road tunnels). This is why there’s a trend toward bigger tunnels, as a cost saving mechanism: BART’s San Jose extension is studying different tunnel approaches, one with a large-diameter tunnel and one with twin small-diameter tunnels, and the cost turns out to be similar. In Barcelona, the large-diameter TBM actually saved money and reduced disruption in construction.
The Boring Company’s various bullet points after its point about tunnel diameter are irrelevant, too. For example, labor is a substantial portion of TBM costs, but in the VLHC study it’s about one third of the cost in easier rock and 15% in harder rock. There appears to be a lot of union featherbedding in some American cities, but this is a political rather than technological problem; without such featherbedding, labor costs are not onerous.
Tunneling Costs Aren’t Just Boring
At $10 billion for just 2.2 km of new tunnel, East Side Access is the most expensive urban rail tunnel I am aware of. The second most expensive, Second Avenue Subway’s first phase, costs $1.7 billion per km, not much more than a third as much. Is New York really spending $10 billion on just boring 2.2 km of tunnel? Of course not. The 2 km in Manhattan cost a little more than $400 million, per an MTA status report from 2012 (PDF-p. 7). The few hundred meters in Queens actually cost more, in an unnecessary tunnel under a railyard. The cavern under Grand Central cost much more, as do ancillary structures such as ventilation.
The TBM is probably the most technologically advanced portion of urban tunneling today. Even in New York, in the most expensive project ever built, the TBM itself is only responsible for about $200 million per km; more typical costs, cited in a consultant’s report for Rocky Mountain tunneling, are somewhat less than $100 million per km. This is why large-diameter TBMs are so appealing: they increase the cost of the tunneling itself, but save money everywhere else by allowing stations to be constructed within the bore.
Of course, The Boring Company is not building conventional subways. Subways already exist, and Musk likes reinventing everything from the wheel onward. Instead, the plan is to build tunnels carrying cars. This means several things. First, the capacity would be very low, especially at the proposed speed (Musk wants the cars to travel at 200 km/h – excessive speed is another of his hallmarks).
Second and more importantly, instead of having to deal with expensive subway stations, the infrastructure would have to deal with expensive ramps. Musk wants cars to be lowered into the tunnels with elevators. Underground elevators are cheap (vertical TBMs are easy), but in the proposed application they just move the problem of ramps deeper underground: the elevator (“skate” in Musk’s terminology) would carry the cars down, but then they’d need to accelerate from a standstill to line speed, in new tunnels, separate from the mainline tunnels so as to avoid slowing down through-traffic. Trains solve this problem by making the entire train stop in the tunnel and taking the hit to capacity, and compensating by running a long train with many more people than cars could possibly hold. But roads would need the same infrastructure of urban freeways, underground.
Switching between tunnel trunks poses the same problem. Flying junctions are expensive, especially underground. In New York, they were common on the IND subway, built in the late 1920s and 1930s; the IND was expensive for its time, around $150 million per route-km in today’s money, whereas the Dual Contracts from the 1910s and early 20s (with fewer junctions) were about $80 million per underground route-km. Most subway systems don’t do what the IND did, and instead of complex junctions they build independent lines, switching between them using transfer stations. With cars, this solution is impossible, forcing underground four-level interchanges; even above ground, those interchanges cost well into the 9 figures, each.
There is So Much Musk Doesn’t Know
The starting point of The Boring Company is that Los Angeles’s tunnel construction costs, which the company pegs at a billion dollars per mile, need to be reduced by a factor of ten. This means cutting them from about $600 million per km to $60 million. While there is nothing that Musk or his company has said in public that suggests he is capable of reducing construction costs, other parts of the world have substantially done so already.
In my construction costs posts, there are a few projects in the $60 million/km area. Manuel Melis Maynar, the former CEO of Madrid Metro, wrote a brief report on how he built subways cheaply; in today’s money, the underground parts of Madrid’s 1999-2003 subway expansion cost around $70 million per km, but this includes rolling stock, and without it, actual cost is likely to be where Musk wants it to be. Recent subway lines in Seoul have also been in that area, including Metro Line 9 and the Sin-Bundang Line. Going up to $100 million per km, there are more lines in Stockholm.
Melis Maynar’s writeup ignores any of the technological pizzazz Musk thinks of. Instead of trying to squeeze more power out of TBM, he emphasizes good contracting practices, and separation of design and construction. Like Musk, he believes that faster construction is cheaper, but he is aware that the limiting factor is not boring speed: even at a conservative rate of 15 meters per day, a TBM could excavate several kilometers a year, so it’s better instead to begin construction at several points along the line and work in parallel rather than in sequence. Adding TBMs does not make projects substantially more expensive: one TBM used for East Side Access cost $6-8 million, and other estimates I’ve seen only reach into the 8 figures, for multibillion dollar projects. Nor does adding staging areas raise cost underground, where there are many potential sites; underwater it’s a bigger problem, and there costs are indeed much higher, but nothing that Musk does seems designed around underwater tunnels, and his proposed map for LA road tunnels is underground.
Musk’s Ideas: Loopy and Boring
Americans hate being behind. The form of right-wing populism that succeeded in the United States made that explicit: Make America Great Again. Culturally, this exists outside populism as well, for example in Gordon Gekko’s greed is good speech, which begins, “America has become a second-rate power.” In the late 2000s, Americans interested in transportation had to embarrassingly admit that public transit was better in Europe and East Asia, especially in its sexiest form, the high-speed trains. Musk came in and offered something Americans craved: an American way to do better, without having to learn anything about what the Europeans and Asians do. Musk himself is from South Africa, but Americans have always been more tolerant of long-settled immigrants than of foreigners.
In the era of Trump, this kind of nationalism is often characterized as the domain of the uneducated: Trump did the best among non-college-educated whites, and cut into Democratic margins with low-income whites (regardless of education). But software engineers making $120,000 a year in San Francisco or Boston are no less nationalistic – their nationalism just takes a less vulgar form. Among the tech workers themselves, technical discussions are possible; some close-mindedly respond to every criticism with “they also laughed at SpaceX,” others try to engage (e.g. Hyperloop One). But in the tech press, the response is uniformly sycophantic: Musk is a genius, offering salvation to the monolingual American, steeped in the cultural idea of the outside inventor who doesn’t need to know anything about existing technology and can substitute personal intelligence and bravery.
In reality, The Boring Company offers nothing of this sort. It is in the awkward position of being both wrong and unoriginal: unoriginal because its mission of reducing construction costs from American levels has already been achieved, and wrong because its own ideas of how to do so range from trivial to counterproductive. It has good marketing, buoyed by the tech world’s desire to believe that its internal methods and culture can solve every problem, but it has no product to speak of. What it’s selling is not just wrong, but boringly so, without any potential for salvaging its ideas for something more useful.