Elon Musk Dismisses Induced Demand, A Phenomenon First Witnessed In 1866

Elon Musk has once again used Twitter to air a controversial opinion. This time the SpaceX and Tesla billionaire has upset urbanists with his dismissal of a phenomenon that was first described in 1866.

On December 29, Musk tweeted that: “Induced demand is one of the most irrational theories I’ve ever heard.”

This was in response to critics who had pointed out that his earlier tweet—“Build super safe, Earthquake-proof tunnels under cities to solve traffic”—was merely describing a subway tunnel.

Musk added: “If the transport system exceeds public travel needs, there will be very little traffic.”

There is very little empirical evidence for this claim, and copious evidence to the contrary, especially in Southern California, where Musk lives, and where the laying down of generous amounts of asphalt has always stimulated motor-vehicle use. (Electric cars get snarled in traffic just as easily as non-electric cars.)

Urbanists have a pithy phrase to describe induced demand:

“Building more roads to prevent congestion is like a fat man loosening his belt to prevent obesity.”

This phrase is based on a 1955 article by Lewis Mumford. Writing in The New Yorker, the great urban planning specialist suggested that “[experts believe congestion] can be solved by increasing the capacity of the existing traffic routes … Like the tailor’s remedy for obesity—letting out the seams of the trousers and loosening the belt—this does nothing to curb the greedy appetite that [has] caused the fat to accumulate.⁠”

Mumford was describing the as-yet-unnamed concept of induced demand in transport. This theory was described in detail in 1969 by J.J. Leeming, a British road-traffic engineer and county surveyor. He observed that the more roads are built, the more traffic there is to fill these roads.

Leeming’s description idea was conceived shortly after German mathematician Dietrich Braess released the Braess’s paradox which demonstrated that “selfish” motorists can not be relied upon to consider the optimal travel times for all rather than just themselves, leading to delays for all.

These ideas were further expanded in the Lewis–Mogridge Position of 1990 and the Downs–Thomson paradox of 1992.

The idea that building more roads leads to more congestion was used by anti-roads campaigners from the 1970s on to combat the futility of road building, and, in the U.K., it briefly became an orthodox position following advice to government from the Standing Advisory Committee on Trunk Road Assessment study of 1994. Prime Minister Margaret Thatcher’s road building program— “the biggest since the Romans”—was halted. (Prime Minister Boris Johnson is widely expected to resurrect this program.)

While Leeming’s study has become an accepted theory among most transport academics, induced demand was known about long before 1969. Writing in 1866, surveyor and engineer William J. Haywood, one of the builders of London’s Holborn Viaduct, said the new thoroughfare would attract more travellers: the “facility of locomotion stimulates traffic of itself,” he wrote.

His solution? Build more roads. This was also the conclusion of Sir Charles Bressey’s Highway Development Survey for London, published in 1937. In his report, Bressey wrote:

“As a typical instance may be quoted the new Great West Road which parallels and relieves the old Brentford High Street route. According to the Ministry’s traffic census extracts … the new route as soon as it was opened carried four and a half times more vehicles than the old route was carrying. No diminution, however, occurred in the flow of traffic along the old route and from that day to this the number of vehicles on both routes has steadily increased…These figures serve to exemplify the remarkable manner in which new roads create new traffic.”

Musk is therefore continuing a long tradition of motoring-besotted experts blithely ignoring the evidence of their eyes.

Houston’s Katy Freeway has 26 lanes at its widest point, expanded between 2008 and 2011 at a cost of $2.8 billion to alleviate severe traffic congestion. The expansion did not alleviate traffic congestion, it made it worse. Travel times increased by 30% during the morning commute and 55% during the evening commute between 2011 and 2014.

Musk’s windshield-view of the world—one of never-ending empty roads—is a pipe-dream, but his “vision” is a mainstream one, with local and national politicians around the world answering the problem of traffic congestion with the magic solution that has never worked: more roads, sometimes in tunnels.

Writing in 1932, the British town planner Thomas Sharp accurately described how some motorists would not be satisfied until every inch of land was capped with asphalt.

“A motorist is apt to complain of the ‘overcrowded’ condition of the road if he finds he has not continually got a whole mile-long stretch of it to himself,” wrote Sharp.

“He will declare there is no pleasure in motoring under such conditions. He will search his map for some alternative route by quiet lanes where he can speed along with the road to himself. And when others find that alternative route and all further alternatives are exhausted, he proceeds to demand a new road system so that his motoring may again become a pleasure.”