Jevons Paradox

William Stanley Jevons
William Stanley Jevons (1835-1882)

I used to live in Houston, Texas and frequently drove on the I-10 West (the Katy Freeway). It is a major commuter highway and was generally badly congested. About five years ago they expanded the Katy Freeway such that the intersection with Beltway 8 is now 26 lanes across. (There used to be a two track railroad on the corridor but they tore it up to make room for more traffic lanes).

katy-freeway-1
The Katy Freeway

I recall that, once construction was complete, travel was much faster and more convenient. But last week I was talking to a colleague who drives the Katy Freeway every day. He was complaining that the traffic was now as bad as ever and could not understand why. The answer to his concern was actually spelled out 150 years ago by William Stanley Jevons (1835-1882). Jevons lived in England at a time when industry was expanding rapidly. In his book The Coal Question: an Inquiry Concerning the Progress of the Nation, and the Probable Exhaustion of our Coal-mines, published in the year 1865, he noted that the coal-burning factories of his time were using fuel more efficiently but, ironically, this led to a greater overall use of coal. A modern expression of his paradox is:

  1. People buy fuel-efficient cars to save money.
  2. Because their cars are more efficient they drive more miles.
  3. Hence the overall consumption of fuel increases.

The same principle applies to the Katy Freeway. Once commute times were reduced developers built many more homes in the Katy area. So more and more people used the newly expanded freeway to the point where it is now as congested as it was ten years ago.

So how does this affect the High Speed Rail project? Well, one of the justifications for the project is that it will relieve some of the traffic pressure on the I-95. People will leave their cars at home and take the new train service. But Jevons Paradox, which is really an expression of the Law of Unintended Consequences, tells us that this will encourage developers to build more homes in suburban Virginia and Maryland, and more businesses will move into the D.C. area. The upshot will be that the I-95 will become more crowded than it is now.

I am curious to know if the High Speed Rail project team has factored the Jevons Paradox into their calculations and what the plans are for managing the potential increase in traffic congestion that this project will create.

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