If you can drive fast in your city, chances are you live in a rich country. Urban travel speed is 50% faster in rich countries than in poor countries, according to a paper by experts at Wharton and elsewhere titled “The Fast, the Slow, and the Congested: Urban Transportation in Rich and Poor Countries.” According to the paper, “richer countries enjoy faster mobility, mainly because their cities have more major roads and wider land areas and both the road infrastructure and the urban footprint of cities grow with economic development.”

“One surprising finding of our study is this strong relationship between mobility and GDP,” said Wharton real estate professor Gilles Duranton, who specializes in urban economics and transportation economics. He co-authored the paper with Prottoy A. Akbar, economics professor at Aalto University, Victor Couture, professor at the University of British Columbia’s Vancouver School of Economics, and Adam Storeygard, economics professor at Tufts University.

“In development circles, [the assumption was that] as a country grows richer, travel speeds will decline because people start buying more cars and congestion will increase,” Duranton said. “But the quality and the number of the roads will also increase, enabling what we call uncongested mobility to increase. This second force is much stronger and dominates rising congestion, which means that mobility increases with GDP.”

What Causes Traffic Jams

Cities of course can be faster and have fewer traffic jams if they have less congestion on their roads. But what makes a bigger difference than congestion is “uncongested speed,” which is possible on roads that don’t have potholes or obstacles such as cattle or pedestrians. In fact, that difference is why richer countries have faster speeds, Duranton said.

To be sure, richer countries will have more cars, and therefore are “moderately more congested” than poorer countries, as Duranton noted. But that congestion is offset by faster uncongested speed. “That trade-off between uncongested mobility and congestion is the second surprising result of our study,” he said. “Everything is driven by uncongested mobility. So, the speed at which you can drive during the day in a given city is mostly driven by how fast you can drive at night, irrespective of congestion.”

Roadmap of the Study

For their study, the experts put together a global database on motor vehicle speed in more than 1,200 large cities in 152 countries that have 96% of the world’s urban population outside China. The sample had data on nearly 19 million trips between June and November 2019. The study simulated more than half a billion instances of these trips on Google Maps to gather information on travel speeds.

That data helped the authors estimate city-level indices of motor vehicle travel speed and congestion. Next, in order to investigate the link between economic development and mobility, they developed a model with travel, road infrastructure, and land area. That model decomposes city size, infrastructure, and topography to explain why urban travel is faster in richer countries. The study builds on an earlier, 2019 paper that Duranton co-authored that focused on mobility in India.

The paper ranked the top 20 cities on six parameters: the fastest, the slowest, the least congested, the most congested, the fastest uncongested speed, and the slowest uncongested speed. It computed those scores using speed indices, a metric designed to capture the number of trips and the price of travel in units of time and other costs such as fuel.

“The speed at which you can drive during the day in a given city is mostly driven by how fast you can drive at night, irrespective of congestion.”— Gilles Duranton

Why Are Richer Countries Faster?

The study underlined the strong relationship between speed and per capita GDP with data on the mileage of major roads and the land area of a city. It found that urban travel speed is faster in cities with more major roads and larger land areas, and cities in richer countries have more major roads and larger land areas.

Cities in richer countries invest more in fast roads, financing that with their higher tax revenues, the paper stated. Their higher incomes also enable more “housing consumption,” or more people to own homes, which in turn reduces population density, the authors added.

But being rich does not necessarily mean being fast. In fact, the fastest city in the study sample, Flint, Michigan, is “a relatively poor city in a rich country,” the paper noted. “Although the relationship between urban mobility and the level of economic development of a country is strong, a higher GDP does not directly increase the speed of travel,” the paper pointed out. In fact, within each country, richer cities are slower. For instance, in the U.S., the higher the average household income in a city, the slower its travel speed.

Congestion and Uncongested Speeds

How rich or poor a country is does not define its congestion levels either, the study found. Bogota, Columbia, leads the list of the 20 most congested cities, but richer places like New York City and London also feature in that list. “Congestion mildly increases with rising income,” Duranton noted. The least congested cities are overwhelmingly from the least developed countries in the study’s sample.

“These are places where there’s so little economic activity, and so few people move with motorized vehicles that the speed at 6 p.m. is not very different from the speed at 2 a.m.,” Duranton said. “At the same time, those places are not particularly fast because they would have uneven or dirt roads, or roads that are permanently encroached by all sorts of users.”

And so, cities with the slowest uncongested speeds are also those with the lowest overall speeds. In the study’s sample, nine of the 10 cities with the slowest uncongested speeds are in poor countries such as Bangladesh, India, and Nigeria. Flint, Michigan leads the list of cities with the fastest uncongested speed. In fact, 19 of the 20 fastest cities are in the U.S.; the other is Windsor, Canada.

Why Is the U.S. So Fast and Bangladesh So Slow?

The U.S. is faster than other OECD countries (the Organization for Economic Cooperation and Development has mostly rich countries) because its cities have “lower populations, wider areas, more major roads, and more grid-like road networks, the paper noted. Compared to other OECD cities, U.S. cities are, on average, less populous, cover more area, have more major roads, and have more roads that conform to the road network’s main grid orientation. U.S. cities are faster than their OECD counterparts also because they have low population density.

Bangladesh, at the other end of the spectrum, is slower than other poor countries because its cities are crossed by more water bodies, are more populous, and have fewer major roads, the paper stated.

“In many parts of the developing world slow mobility mainly results from poor infrastructure.”— Gilles Duranton

Tackling the Causes of Traffic: How to Improve Urban Mobility

Congestion pricing, or levying tolls on vehicles during peak hours, is one option cities have considered. In New York City, for instance, the Metropolitan Transportation Authority plans to levy a toll from the Spring of 2024 on vehicles passing through Manhattan’s central business district. “While desirable, it may not be the best way to do it everywhere,” Duranton said, “since in many parts of the developing world slow mobility mainly results from poor infrastructure.”

One option for large cities is to invest in not just the major roads but also in secondary and tertiary roads that can share the congestion load, Duranton said. Building vertically — with flyovers, as in South Korea and Japan — or underground tunnels, is another option, but can be cost-prohibitive, he added. For example, Tesla CEO Elon Musk’s plan to build a high-speed transport system that could cover the distance between New York and Washington, D.C. in 29 minutes is “economically impossible,” he noted. For their next research paper, Duranton and his co-authors plan to study urban transit in cities.

There is no silver bullet to improve urban mobility, but policymakers have to judiciously weigh the cost of space and the pollution impact of making more room for cars, Duranton said. “I’m all in favor of building more infrastructure for roads and private motorized vehicles in many parts of the world, but in places where the cost of space is so incredibly large, cars should not be prioritized because they take a lot of public space and this public space is very expensive.” For example, if the space occupied by a car traversing for an hour along Manhattan’s Fifth Avenue were to be benchmarked against the price of retail real estate on that stretch, “we would be talking of charging more than $100 an hour,” he added.

Poor countries have to get their basic infrastructure right before worrying about things like congestion. “In the poorer parts of the world, it’s about building up the grid, planning for urban expansion, and having a plan of what the infrastructure will look like in 20 years when their cities have populations that may be two or three times bigger than today,” Duranton said. Faster transportation calls for not just more roadways but also lower density, so those poorer countries should also invest in expanding housing infrastructure, he added.

Why the Study’s Findings Are Important

“There is a previously undocumented, first-order relationship between a country’s economic development and the speed of vehicular travel in its urban networks,” the paper stated of its central finding.

Duranton and his co-authors pointed out that their findings are important for three reasons. First, urban transportation policy is a major concern worldwide, and the study’s results “emphasize several effects relevant for policy.” Second, while cities are expected to reduce the distance between people and facilitate interactions, “many urban dwellers do not live within walking distance of good jobs, good schools, productive peers, and attractive entertainment options.” Third, the study fills a knowledge gap as “little is known about how most cities fare in terms of mobility,” the authors observed. “Urban policymakers rarely know how their city performs relative to peer cities and why.”