The Fast, the Slow, and the Congested

That is a new NBER working paper by Protty A. Akbar, Victor Couture, Gilles Duranton, and Adam Storeygard.  Here is the abstract:

We assemble a new global database on motor vehicle travel speed in over 1,200 large cities in 152 countries. We then estimate comparable city-level indices of travel speed and congestion. Most of the variation in urban travel speed is across countries, not within. National income per capita explains most of this cross-country variation in speed. In rich countries, urban travel is roughly 50% faster than in poor countries. To investigate the link between economic development and mobility, we develop an urban model with endogenous travel, road infrastructure, and land area. The model provides an exact decomposition of how city size, infrastructure, and topography contribute to explaining why urban travel is faster in richer countries. We find that richer countries are faster, mainly because their cities have more major roads and wider land areas. These effects operate by increasing uncongested speed, not by reducing congestion.

In general, I am much more skeptical about slower modes of transportation than are many other MR readers, most of all those on the Left.

If you look on p.36, “major road length” is the variable most predictive of speed if you ask why rich countries are faster than are poor countries — please do not forget the Lucas Critique however!  After all, they do measure Flint, Michigan as the fastest city [sic] in the world.

Here is a good paragraph (p.37):

Compared to other cities in the oecd, us cities are (exp(−0.27) − 1 =) 24% less populous, cover 72% more area, have 67% more major roads, and have 30% more roads that conform to the road network’s main grid orientation. Panel A of figure 5 reports the corresponding decomposition result. The low density of us cities explains most of why they are faster. Major roads matter too, as do griddier road networks. City size variables account for 47% of the speed difference between the us and other oecd countries, infrastructure accounts for 35%, and the share accounted for by topography is negligible.

If you are wondering, by their measures Dhaka is the slowest city in the world.

An excellent paper, recommended.