CALIFORNIA’S high-speed railway—the largest public-works programme currently underway in America—overcame a serious challenge on March 25th, which would have taken bonds issued to help pay for the railway and reallocated the money to water projects. Unable to collect enough signatures to put the proposition on next November's ballot, the backers have now postponed the measure for two years. Had it been successful, the proposal would have dealt a death blow to the high-speed rail project by deleting its biggest single source of funding.

That is the second time in recent weeks that the $64 billion high-speed rail project linking Los Angeles to San Francisco has come close to being stopped in its tracks. What promised to be the most serious of a number of law suits threatening to derail the project was thrown out by a superior court in Sacramento on March 8th. There was no evidence, the judge concluded, that the California High-Speed Rail Authority had failed to meet its statutory obligations, as the plaintiffs alleged. The court, nevertheless, left the door open for the case to be reheard at some future date.

The suit brought by Kings County Board of Supervisors and two Central Valley farmers accused the rail authority of violating restrictions imposed by a ballot held in November 2008 (Proposition 1A) that approved a $9.95 billion bond issue to help pay for the high-speed railway. Voters were told at the time that the project would cost no more than $33 billion, with the federal government stumping up $3.2 billion and private investors chipping in the balance. So far, such private investors have been conspicuous by their absence.

According to the Proposition 1A Bond Act, the high-speed rail project has to be financially viable; trains have to operate (without subsidy) every five minutes in either direction during the day; and funds for each segment of the route need to be identified before work on the leg in question can commence. Above all, trains have to make the 520-mile (840-km) journey between the Los Angeles basin and the San Francisco in two hours and 40 minutes, reaching speeds of 220 mph (350 kph). As for ridership, the rail authority reckoned some 65m to 96m passengers per year would be travelling the route by 2020. The basic fare was to be $55 one way.

That was all pie in the sky, a way of selling the deal to voters in 2008. A review in 2011 put ridership at a more realistic 30m passengers a year, with an end-to-end ticket price of $89. Meanwhile, the overall cost of the project had soared to $98 billion. And instead of going into service by the end of the decade, the high-speed railway would not be ready until 2033.

The uproar that ensued prompted a shakeup along with some hurried rethinking. The cost was subsequently pegged at around $68 billion for the first phase of the network, with an opening date in 2029—almost a decade later than originally promised. A second phase, involving track extensions to Sacramento in the north and San Diego in the south, would follow if and when money became available. The draft 2016 business plan has now trimmed the cost of the first phase to $64 billion.

While private funds have shown little interest, at least the project’s finances are no longer quite as gloomy as they were a year or so ago. Jerry Brown, California's govenor and a stalwart supporter of the high-speed train, strong-armed the legislature in Sacramento into allocating it 25% of the state’s annual “cap and trade” proceeds from auctioning off carbon credits to big polluters, which are currently worth around $1 billion a year. As a result, the rail authority has now identified the $21 billion required for building the project’s initial leg (San Jose to the Central Valley). It still needs a further $43 billion before it can start work on extending the line north to San Francisco and south towards Los Angeles.

With the rail authority’s finances resolved for the time being, opponents have focused instead on the project’s legal requirement to cover the distance between Los Angeles and San Francisco in two hours and 40 minutes. The rail authority claims (optimistically) that such a time remains doable, though cost-saving measures have forced the high-speed train to share tracks with slower-moving freight and commuter services in the Los Angeles basin and the Bay Area.

What also remains in doubt is just how many people will actually ride the high-speed network. In revising its revenue model, the rail authority has incorporated findings from surveys on rider preferences, along with forecasts of California’s likely population, housing and employment growth. The data were then crunched using Monte Carlo simulations to minimise the risks of being wrong. The analysis suggests that, based on a confidence level of 50%, the service will have some 28m passengers by 2029, generating $1.3 billion of revenue. However, as thorough as this analysis is, unanswered questions remain.

Above all, what is it that California’s railway planners know that their Japanese counterparts do not? The former state-owned Japanese National Railways and its partially privatised regional replacements have struggled for decades to make their high-speed Shinkansen (“bullet train”) routes profitable. Japan’s eight Shinkansen lines have little in the way of competition, thanks to over-crowded roads, expressways that charge exorbitant tolls and limited air services. Even so, only one Shinkansen service—JR Central’s 550-km line between Tokyo and Osaka—makes anything like a decent enough operating surplus to cover its costs, make necessary investments and pay a modest dividend.

It does so for one simple reason: the volume of traffic it carries—some 140m passengers a year. The Tokyo plain (Kanto) is home to 42m people, while greater Osaka (Kansai) has 23m. Between these two huge population centres reside a further 10m people in conurbations like Hamamatsu, Nagoya and Kyoto, all served by the Tokaido Shinkansen. At peak hours, trains leave Tokyo Station bound for Shin-Osaka and beyond on average every four to five minutes, and every seven to eight minutes for the rest of the day. The latest Nozomi (limited stop) service whisks passengers between Tokyo and Osaka in two hours and 22 minutes.

Compare that with California. As sprawling as it is, the Los Angeles basin has a population of just 18m. The nine counties surrounding the Bay Area have a little over 7m residents between them. The farming communities astride the proposed high-speed rail line through the Central Valley have a combined population of around 1m. In short, California’s high-speed railway is attempting to do what the Tokaido Shinkansen does, but with a third of the number of potential passengers, on a route that is half as long again. California’s taxpayers will pay dearly for Mr Brown’s high-speed legacy.

If there are serious doubts hanging over a conventional high-speed train operating at speeds up to 220mph between Los Angeles and San Francisco on conventional electrified track, what then are the prospects for Elon Musk’s proposed 760mph Hyperloop between the two cities? The short answer is probably none. Even so, Mr Musk’s flare for publicity has done much to capture the imagination.

Back in 2013, the billionaire boss of the Tesla electric-car company and the SpaceX rocket developer hit the headlines with a fresh take on the “transplanetary subway” proposed in the 1970s by visionaries at Rand Corporation, a think tank in Santa Monica, California. However, instead of being under the ground, the Hyperloop proposed using a steel tube containing a near-vacuum that would sit on stilts above it. Passenger pods, riding on air-bearings or magnetic fields instead of wheels, would travel inside this air-tight tube, to be laid alongside the Interstate-5 highway between Los Angeles and the Bay Area, at close to the speed of sound, completing the 400-mile journey in little over half an hour. Mr Musk reckoned the Hyperloop could be built for no more than $6 billion—a tenth the cost of the California high-speed train.

Two separate groups have taken him seriously. Hyperloop Technologies (HT), in central Los Angeles, is a typical startup venture, with 30 or so full-time employees and $10m of seed money. By contrast, Hyperloop Transportation Technologies (HTT), based on the west side of the same city, is a crowd-sourced community of 450 volunteers scattered around the country, who devote ten hours a week to the project in exchange for stock options.

They are not the only ones mesmerised by the Hyperloop idea. Some 116 student engineering teams, from across America and elsewhere, gathered at Texas A&M University late in January to show off their Hyperloop pod designs in a competition organised by SpaceX. Finalists have been invited to test prototypes this summer on a five-mile test track being built by HTT at Quay Valley, California.

Everyone involved now accepts that Mr Musk seriously under-estimated the cost of building a Hyperloop between Los Angeles and San Francisco—probably by a factor of ten or more. There are few illusions, too, about the engineering difficulties involved. Fabricating an air-tight steel tube hundreds of miles long, with solar-powered linear motors providing propulsion while supporting passenger pods on air-bearings or by magnetic levitation is challenging enough. A bigger hurdle is overcoming the “pistoning” effect, caused by air in the tube (even though it would be at only a thousandth the pressure of that outside) piling up in front of the pod and slowing it down. Calculations done by NASA suggest the tube would have to be at least four times wider than the pod to prevent even the tiny amount of residual air within it blocking the pod's passage. Mr Musk budgeted for tubes only twice as wide.

But perhaps the most intractable problem facing Hyperloop designers is how to deal with not just the jostling, vibration and noise bombarding passengers as the compressed air screamed around the pod, but also the g-forces involved. These could easily exceed a queasy 0.5g as a result of slight variations in alignment caused by the tube’s supports flexing and settling. At the speed it is designed to travel, the Hyperloop could be a veritable “vomit comet”. A far better case could be made for it as a means for funneling freight to market (fresh produce from the Central Valley?) than as a fairground ride for churning the stomach.

If the ride quality alone did not render the Hyperloop a non-starter, the cost of building it certainly would. Michael Anderson, a resource economist at the University of California, Berkeley, reckons it would cost around $100 billion to complete. While Governor Brown’s legacy may now be safe, albeit at considerable public expense, there is no way that the Hyperloop would ever work out, says Dan Sperling, director of the Institute of Transportation Studies at the University of California, Davis. It would make even the high-speed train look a bargain.