Elon Musk started The Boring Company in late 2016 because he was frustrated by sitting in his car in Los Angeles traffic. A system of tunnels, he reasoned, would alleviate certain traffic choke points. The idea turned into reality throughout 2017, as Musk tore up the parking lot outside of his SpaceX headquarters, testing boring machinery to find weak spots that engineers might improve upon to make tunnel-digging faster and cheaper.

The idea also changed a bit: instead of simply looking to build the cheapest tunnels, The Boring Company wanted to build a "Loop" inside its tunnels. The Loop would be a modified version of Musk's Hyperloop idea, but it would not pull a vacuum, and cars would be lowered into the tunnel system where they would be put on electric skates and zipped off to their destination automatically.

According to some tweets from Elon Musk last night, though, the idea has once again morphed. "Adjusting The Boring Company plan: all tunnels & Hyperloop will prioritize pedestrians & cyclists over cars," the executive tweeted, adding: "Will still transport cars, but only after all personalized mass transit needs are met. It's a matter of courtesy & fairness. If someone can't afford a car, they should go first."

Does this sound exactly like a subway? Yes. It does. But Musk says this idea will be slightly different. He tweeted: "Boring Co urban loop system would have 1000s of small stations the size of a single parking space that take you very close to your destination & blend seamlessly into the fabric of a city, rather than a small number of big stations like a subway."

Granted, people who live in Manhattan or Paris might feel that their subway system has an adequate number of stations, but many large cities in the US have subway or light rail systems with poor station density, and a system that transports cars as well could have an advantage.

Still, the main problem with building massive infrastructure for public transportation is not generally a problem of technology, it's a problem of politics. A sad example is the California High Speed Rail project. On Friday, the Los Angeles Times reported that the bullet train intended to link Los Angeles and San Francisco in three hours had dramatically missed deadlines and blew through budget limits. In 2014, project operators estimated they would have a system up and running by 2021. Now the system may not be fully operational until 2033. The original project was supposed to cost $33 billion. Yesterday, the Times estimated that the cost will come to $77.3 billion and could rise as high as $98.1 billion. Contributors to that rising cost include years of delays, lawsuits to hinder or stop the project, and opposition from communities that don't want a rail system passing through.

A system of small tunnels could bypass some of the aesthetic concerns that communities might have, but it may not eliminate some of the structural concerns. Of the California High Speed Rail project, the Times wrote: "The cost of environmental reviews jumped from a projected $388 million in 2010 to more than $1 billion. The rail authority found that nobody could be sure what was under the ground in Fresno [a California city through which the bullet train would pass], driving up the cost of relocating sewers, water lines, communications cables, and electrical conduits by hundreds of millions of dollars."

For now, The Boring Company seems to be making connections with authorities in Maryland, Chicago, and Los Angeles. Until any real digging starts, it's hard to tell if this will become as real as SpaceX or Tesla, or just vapor infrastructure. (To his credit, Musk appears to be self-aware about this, tweeting a poll that asks whether tunnels are an "impossible pipedream" or a "stupid hole in ground" or "both.")

Until then, the CEO tweeted a video rendering of what a Loop station might look like: