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Tuesday, January 5, 2016

Why Commutes Aren't Twice as Long in Cities With Twice the Population

You probably don’t love your trip to work, but researchers have identified three reasons it’s not much, much worse.


By Eric Jaffe, January 4, 2016

 Image joiseyshowaa / Flickr

It’s no surprise that larger cities are more productive cities. As a metro area expands it becomes home to a stronger labor market: workers can pick from more and better jobs, and jobs can choose from more and better workers. Meanwhile the collective powers of an urban environment—the ability to share knowledge and basic infrastructure, for instance—give rise to greater wealth and ideas than population growth alone would predict.

What is a little surprising is that even as cities get larger, life in them doesn’t necessarily grind to a halt. Sure, it can sometimes feel like that’s the case when you’re stuck in rush-hour gridlock. But while traffic congestion may be a personal annoyance, it’s also a broad indication of a healthy economy. If it’s easy for you to drive right downtown at 9 a.m. on a Monday, there probably isn’t much downtown to do.

Take the comparative example of New York and Chicago circa 2000. New York at that time had more than twice Chicago’s population and nearly twice the jobs: 7.6 million to 3.9 million. But it didn’t have twice the commute trouble. On the contrary, workers could reach 85 percent more jobs in New York than in Chicago within an hour (6.2 to 3.6 million) and 82 percent more jobs within a half hour (3.7 to 2 million).

In other words, the friction of New York’s heavy commuter activity only slightly compromised the power of its labor market. And New York is no outlier in this case. A productivity analysis of 40 U.S. metros of varying populations, conducted by Shlomo Angel and Alejandro Blei of
 the Urbanization Project at New York University, found that cities with twice the number of jobs sustained a labor market nearly double in size within a “tolerable” commute of 30 (87 percent), 45 (94 percent), or 60 minutes (97 percent).

The reason bigger workforces don’t translate into total stagnation is that metros have “nimble and self-adjusting commuting patterns” that preserve their economic advantage, report Angel and Blei in a paper in the journal Cities. Those patterns have three key components: density, job and home relocation, and overall mobility. Together these forces keep commute time growth to a tolerable 7 percent, on average, in a city with twice the population of another one—instead of the awful 41 percent expected by mathematical calculations.

The three key factors

The role of density is straightforward. When homes and jobs are clustered together, commuters don’t need to travel as far to reach either one. Angel and Blei find that, among their sample of 40 U.S. metros circa 2000, density helps cities with twice the population fit into just 70 percent as much area, on average. In these cities, densification reduces the growth of commute lengths to 30 percent from the expected 41 percent.
Densification helped cities with twice the population of smaller ones take up just 70 percent more area, on average. (Angel and Blei, Cities, 2015)
Then there’s relocation by both parties. On the employee end, workers don’t tend to move unless their job falls outside a tolerable commute range, in which case they typically move closer to work, not farther away, according to Angel and Blei’s analysis. Businesses, meanwhile, moved closer to key employment pools in the 40 cities included in this study, reflecting the recent emergence of multiple metro area job centers and reduced reliance on a central business district for jobs.

Together these moves result in an average commute distance just 13 percent larger in a city with twice the population—rather than the 30 percent increase expected from densification alone.
Home-work commute maps show that job corridors exist across a given metro area—not just through the central business district. (Angel and Blei, Cities, 2015)
Finally, Angel and Blei found that commuting times grew at a slower rate than commuting distances in larger cities as a result of greater mobility. They attribute these savings to traffic in larger cities shifting from low-speed arterial roads to higher-speed (and ever-expanding) freeway systems. (The researchers focused on metro area road networks, given that the overwhelming share of Americans still drive to work alone, but previous work has shown that public transport plays an integral and enormous role in urban agglomeration economies, too.)

So commute times rose just 7 percent in cities with twice the population of a smaller one—half the 13 percent rise expected after the combined effects of densification and relocation are taken into account.
Commutes time in the study sample increased just 7 percent in cities with twice the population, in part due to greater mobility. (Angel and Blei, Cities, 2015)

What it means

All told, density, relocation, and mobility reduced expected commute times in a large metro area by a factor of six, relative to one half its population size. For those keeping close score at home: density contributed to 25 percent of the reduction, relocation 41 percent, and mobility 34 percent. Angel and Blei conclude with some broad policy suggestions for urban planners: help people find affordable homes near work, help businesses relocate near workers, and help commuters get from home to office.

“In a way, we call for a rebirth of ‘regionalism’ or ‘metropolitanism’ at the expense of the celebrated ‘localism’ of today,” Angel tells CityLab via email. “It is still difficult to implement fair housing policies in American metropolitan areas. It is difficult for poor people to move to suburbs that still practice exclusionary zoning. It is still difficult to find grid-like bus networks that get people to and from work quickly and efficiently.”
The analysis has many limitations. By focusing on data from 2000, for instance, it fails to capture the past decade of city center growth. By focusing on road networks it undervalues the role of balanced transport systems, the need for all-day urban transit, and the social and economic costs of excessive road expansion. And by focusing on a group of cities it can’t isolate whether, say, a heavily sprawling city like Atlanta fared better or worse than a concentrated place like Chicago or New York.

The work also offers some mixed planning messages. On one hand, the benefits of density and mobility suggest a need for compact development near transit lines; on the other hand, the benefits of freeway speed would seem to endorse a transportation status quo that centers on car travel. Angel prefers to focus on the bigger picture: local initiatives that make commuting less tolerable might reduce overall productivity—and right now, for better or worse, commuting in American metros mostly means driving.

“The only realistic future, as far as I see, is replacing the car with driverless cars that are less polluting, require less road space and less parking space, and offer services for the car-less,” he emails. “Compact development along transport corridors is fine and I have nothing against it, but it is certainly not a comprehensive solution for cities that now have three out of four jobs outside these corridors.”