In other words, we show that investments in highways did not effectively relieve traffic congestion. This suggests that expansion of the highway network induced the demand for car travel, and so, on average, the level of congestion remained roughly unchanged in the period 1985–2005. The results indicate that this elasticity is in the range close to 1. We use data for the 545 largest European cities to estimate the elasticity of a measure of congestion with respect to highway expansion. The best estimate is that the elasticity of travel with respect to capacity is essentially unitary: a one percent increase in highway capacity generates a one percent increase in vehicle travel. They find very similar results, confirming the fundamental law of road congestion. Three researchers from the University of Barcelona use two decades of data for hundreds of European cities to replicate the methodology used by Duranton and Turner and Hymel in the U.S. The latest evidence of the universality of the fundamental law comes from Europe. Europe: Still more evidence Induced Demand and the fundamental law of road congestion Hsu and Zhang found a nearly identical result for roadway expansion projects in Japan. Two recent and definitive studies are Duranton and Turner’s “ Fundamental Law of Road Congestion,” and more recently Kent Hymel’s “ If you build it they will drive” both of these studies use data for the US and find a unit elasticity of traffic with respect to roadway expansion. Urban highway expansion is the labor of Sisyphus. Simply put, expanding road capacity is a futile, and self-defeating effort. Sophisticated, in-depth studies of transportation infrastructure and traffic levels, that look at entire nations and measure traffic changes over decades find what is now being called “the fundamental law of road congestion.” An increase in road capacity directly generates a proportional increase in traffic, with the effect that congestion and travel times quickly return to (or worsen from) pre-expansion levels. It’s been successively widened many times, most recently at a cost of $3 billion, and within three years of its expansion, commute times were even longer than before.īut there’s much more than anecdotes like the Katy Freeway to buttress the observation of induced demand. Induced demand: More road capacity produces more trafficĪt City Observatory, we’ve related the classic example of North America’s widest freeway, the 23-lane Katy Freeway in Houston. The fundamental law of road congestion requires us to fix broken traffic models and stop widening highways in a futile effort to reduce congestion.Ĭall it what you will: Jevons Paradox, Braess Paradox, Marchetti’s Constant or Downs’ Triple Convergence, the science confirms them all. The best available science worldwide-in Europe, Japan and North America-shows a “unit-elasticity” of travel with respect to capacity: A 1 percent expansion of capacity tends to generate 1 percent more vehicle miles traveled. Studies from around the world have validated the existence of induced demand: each improvement to freeway capacity in urban areas generates more traffic.
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