We covered Elon Musk's earlier musings about building a tunnel and were somewhat dismissive; it just seems odd to have someone who sells cars complaining so much about traffic. It was a cute story but nobody really took it seriously. But in fact, Mr. Musk is still at it, still making plans, tweeting away:
Exciting progress on the tunnel front. Plan to start digging in a month or so.— Elon Musk (@elonmusk) January 25, 2017
Alas, it is not a Time Tunnel, which might make a difference. He told the Verge in a direct message:
Without tunnels, we will all be in traffic hell forever. I really do think tunnels are the key to solving urban gridlock. Being stuck in traffic is soul-destroying. Self-driving cars will actually make it worse by making vehicle travel more affordable.
There are a couple of issues in this statement. First, there is pretty good evidence that building a tunnel won't make a whole lot of difference, because of The Fundamental Law of Road Congestion, studied by Gilles Duranton and Matthew Turner of the University of Toronto:
We investigate the relationship between interstate highways and highway vehicle kilometers traveled (vkt) in us cities. We find that vkt increases proportionately to highways and identify three important sources for this extra vkt: an increase in driving by current residents; an increase in transportation intensive production activity; and an inflow of new residents.
In other words, if you build more highways, more lanes and more tunnels, it attracts more cars and fills them up fast. And as anyone who has been stuck in a tunnel into Manhattan can tell you, that is even more soul-destroying than being stuck above grade in your car. You can't even get a signal on your cell phone. But it is inevitable, because of "induced demand", described by Jeff Speck in his book Walkable City:
The main problem with traffic studies is that they almost never consider the phenomenon of induced demand. Induced demand is the name for what happens when increasing the supply of roadways lowers the time cost of driving, causing more people to drive, and obliterating any reductions in congestion.
Charles Marohn also put it nicely: “Trying to solve congestion by making roadways wider is like trying to solve obesity by buying bigger pants.”
In Elon Musk's California, UC-Davis scholar Susan Handy studied induced demand and came up with some conclusions that were published in CityLab:
- There’s high-quality evidence for induced demand. All the studies reviewed by Handy used time-series data, “sophisticated econometric techniques,” and controlled for outside variables such as population growth and transit service.
- More roads means more traffic in both the short- and long-term. Adding 10 percent more road capacity leads to 3-6 percent more vehicle miles in the near term and 6-10 percent more over many years.
- Much of the traffic is brand new. Some of the cars on a new highway lane have simply relocated from a slower alternative route. But many are entirely new. They reflect leisure trips that often go unmade in bad traffic, or drivers who once used transit or carpooled, or shifting development patterns, and so on.
The LA Times is sanguine about the legalities of building a tunnel:
...building a massive tunnel in the Southland could be harder than rocket science considering the bureaucratic nightmare Musk would face gaining approval from multiple municipalities, not to mention the existing infrastructure he would need to avoid and the stupendous cost (the first phase of New York City’s newly opened Second Avenue subway cost $4.5 billion for just two miles of track and three stations).
However Elon Musk has shown time and time again that when he has an idea, stuff happens. So we may be driving our Teslas in tunnels sooner than we think.