I’m no genius, but Elon Musk certainly is. After all, the 46-year-old inventor and investor shoots rockets into space, talks confidently of colonizing Mars, and has built in Tesla a car and solar energy company that the market values at tens of billions of dollars despite it having yet to turn a profit.

But I believe I know something that Musk doesn’t: Transportation systems don’t just get us from point A to point B. They shape the entire way cities look and feel and grow.

Let me back up a bit. One of Musk’s current big ideas is to build a vast network of tunnels underneath greater Los Angeles. Cars riding on wheeled platforms called “electric skates” would speed along at more than 120 miles per hour. “You should be able to get from, say, Westwood to LAX in five or six minutes,” Musk said in a TED Talk interview earlier this year. That drew great applause from the audience: Interstate 405, the highway that now carries most traffic the 10 miles between the Los Angeles neighborhood and the airport, is the nation’s most congested.

This vision is not just a pipe dream. His tunnel-boring company -- called the Boring Company, of course -- has already been given permission to dig a 1.6-mile test tunnel underneath Hawthorne, Calif., where the company is headquartered. It’s now under construction. (The Boring Company was also recently given permission to dig a 10.1-mile tunnel in Maryland as part of Musk’s proposed “hyperloop” transportation system.) Crucial to Musk’s idea is that he envisions developing cheaper tunnel-boring technology -- so cheap that one could essentially build an infinite number of tunnels underground. “You can alleviate any arbitrary level of urban congestion with a 3D tunnel network,” Musk has said.

But while the engineering vision is incredible, Musk doesn’t seem to know much about how transportation affects what is around it. Musk, like many people, apparently thinks of transportation simply as getting from one place to another. But as I wrote in my first book, How Cities Work: Suburbs, Sprawl and the Roads Not Taken, if you create a well-used new way of moving, you create a new way of living. Subways created subway cities. Streetcars created streetcar suburbs. The postwar interstates created linear cities along the superhighways’ spines. And Los Angeles’ elevated freeways and limited-access roads created sprawling neighborhoods below that, to this day, people both love and love to hate.

With this in mind, you can see where Musk goes wrong. He talks of the built environment as if it were static -- as if you could have all of these tunnels going between places and nothing would change up on the ground.

But of course if you had high-speed tunnels under Los Angeles, developers would build to dovetail with them: things like apartments, office buildings and retail. Churches and schools would spring up in new places. Musk envisions his tunnels as helping get people to Pasadena in minutes. But if these tunnels really work, then Pasadena would have new residents living there, and it and wouldn’t be like present-day Pasadena anymore. Giant parking garages might develop above tunnel stations. Or if some driverless car scenario minimizes the need for parking, even-denser collections of apartments and shopping and office centers would come.

Sure, Musk’s envisioned L.A. tunnel system looks pretty cool. An animated video on the Boring Company website shows what looks like a Tesla sports car in torturously slow regular traffic on a city street. Then, like some Q-designed vehicle in a James Bond movie, the car rolls onto an electric skate in the parking lane. The skate drops down beneath the surface and is ferried off to the tunnel system. The skate-carried car rockets along at a breathtaking speed until it is delivered back up to a surface street, where the driver continues on his or her journey.

But you can see the shallowness (forgive the pun) of Musk’s thinking in that in the videos these deep tunnels have only a light amount of traffic in them. In the real world, of course, they would fill up very quickly. I was reminded of the influential Swiss architect and planner Le Corbusier from the 1920s, whose sketches of his proposed new cities of towers showed only a few cars on their highways. We all know how that worked out.

I was curious as to what Musk or an associate would say about my criticisms, but I couldn’t get anyone to talk to me. I did reach a Boring Company spokesperson, who referred me to their website’s FAQ section. There, I found a very interesting discussion about the engineering aspects of the tunnels, but nothing about land use.

So how could a new layer of cheaper tunnels be put to more beneficial use than what Musk envisions? Well, it may not sell many Teslas, but one answer might be a more complete subway or bus system, combined with bicycling and walking networks aboveground. The nice thing about those is that we have a history of pleasant urban spaces being built around them and some models to work with.

Whatever is done, one should always remember that transportation determines land use, either by design or in unintended ways. Another lesson is that one should be wary of geniuses bearing gifts. They may be well-intentioned, but they may not know everything about what their packages contain.