Are road diets the next big thing for US cities?

Does Chicago really need all those lanes? Image: Getty.

Like so many new concepts in urban planning, road diets seem like a great idea at first. And, like so many concepts in urban planning, they tend to generate a lot more criticism once they’re put into place.

The idea of a road diet is simple: to pinpoint streets that have excess capacity and could be narrowed down without significant car congestion, so providing space for other uses, such as sidewalks and bike paths.

It’s also an almost exclusively American concept, which makes sense; while streets in Britain and other European countries aren’t exactly crying out to be narrowed down, on the other side of the Atlantic, the streets seem to be the only thing wider than the country’s waistlines.

The roots of the concept date back to the 1970s, but it only began gaining traction over the past decade, loosely connected with other movements such as smart growth and complete streets.


Planners in the US began studying cases in which city streets had been widened to improve traffic flow for cars. They found that, in most cases, these projects did little to improve traffic flow, while creating an enormous increase in accidents. For instance, a study done in Fort Madison, Iowa, showed that while widening a main road led to a traffic volume increase of 4 per cent, it also increased the accident rate 14 per cent, and the injury rate by 88 per cent.

The obvious response to these findings is, naturally, to slim wider streets back down. But this slimming down can take many forms: widened sidewalks; replacing four-lane highways with three-lane ones, in which the middle lane is for those turning; and separated bike lanes. Last year, urban planner and author Jeff Speck teamed up with animation specialist Spencer Boomhower to create a series of videos showing the many possible forms road diets can take.

How effective has the concept been? In the US, road diets have seen a number of success stories. In New York City, a 2013 study revealed that road diets there had “significant safety benefits”.  They’ve seen success on the west coast, too: a pioneer in road diets, San Francisco has implemented 34 road diet projects over the last four decades, with favourable reactions from traffic engineers. Similar projects have also been implemented successfully in nearby Davis, California.

A street in Davis, CA, before its road diet. Image: Transport Observer/Wikimedia Commons.

But though road diets have allowed some cities to slim down their traffic safety problems, others have found that sticking to road diets is harder than sticking to actual diets.

Take Carolina Beach, North Carolina. Back in 2010, planners implemented a road diet on Lake Park Boulevard, one of the city’s main thoroughfares, in a bid to make the city more bike friendly.

But the measure was met by howls of protest. Local businesses complained of decreased sales, and the city’s car traffic during holidays led to increased traffic jams. In 2012, the road diet was reversed.  

Down the coast, in Gainesville, Florida, a road diet was adopted in mid-2013 for a wooded stretch of 8th Avenue. Four traffic lanes were reduced to two on a trial basis.

While the trial decreased injuries significantly, it met with staunch criticism from drivers, inconvenienced by a difficult merge area created by the road diet. The new configuration remained for over a year, but it was finally removed after being voted down by the city commission in December 2014, though plans are in the works for adding a shared pedestrian/cycle path on both sides of the road.

The same street after its road diet. Image: Transport Observer/Wikimedia Commons.

Then there’s Los Angeles, which despite some noble efforts to reverse its car-centric status by expanding its metro system, lives up to its reputation in its efforts to pursue road diets. Back in 2011, an attempt to implement a road diet on Wilbur Avenue, deep in the depths of the suburban San Fernando Valley, was quickly put to sleep after massive neighbourhood outcry.

Even in Silver Lake, an LA neighbourhood packed with bike-loving hipsters, the policy is in trouble. A road diet on Rowena Avenue in place since 2013 has been the source of continuous controversy, including angry driver rants caught on tape, though it remains in place for the time being.


Though the reasons road diets fail vary city by city, their common underlying cause boils down to political convenience. By their nature, road diets create an immediate inconvenience for drivers – who tend to be more affluent and politically connected; to compensate that, there’s only the long-term promise of creating greater safety, and a more bike and pedestrian friendly urban environment. For local politicians eager for quick victories, this all too often proves to be a toxic combination.

The lesson is clear. Road diets have paid off for some US cities. But for others, powerful political forces and a deeply rooted car culture have made sticking to road diets as difficult as swearing off junk food.

 
 
 
 

Where are the world's largest cities?

An astronaut's eye view of urbanisation. Image: Getty.

Every year or so, Demographia, the St. Louis-based consultancy, publishes the World Urban Areas Report – a sort of bumper book of city population stats.

The report is a veritable treasure trove of demographic stats for city nerds. If you want to know whether, say, Edinburgh is one of the 1,000 biggest cities in the world, then Demographia will tell you. (It's not, it's just outside at joint 1017th). And if you want to know whether Paris covers a bigger land area than London, it'll tell you that, too. (It does: 2,845km2, as opposed to 1,738 km2.)

It even includes estimates for the size and density of hundreds of towns so tiny that you're slightly surprised to find that anyone on the other side of the Atlantic has even noticed they exist. (Favourite example: Kidderminster*.)

But the most fun is to be found in the first half of the report. Table 1 includes the 1,022 built-up areas in the world that house 500,000 people or more, ranked in order of population; Table 2 ranks the same cities in order of land area.

I don’t know about you guys, but we are stoked.

via GIPHY

(*55,000 people in 16 km2, giving a population density of 3,400 per km2, since you ask.)

Understanding the numbers

Explanations first. The report defines urban areas as

...a continuously built up land mass of urban development that is within a labour market (metropolitan area or metropolitan region)... [and] contains no rural land.

We should probably also note the reports caveat, about the limits of its own methodology:

Revisions are made as more accurate satellite photographs and population estimates become available. As a result, Demographia World Urban Areas is not intended for trend analysis.

Year-to-year changes indicated in population and land area may merely reflect better data that was not used before and may not, therefore indicate a trend.

In other words, if this year's report has a larger estimate for a city's population than last year's report, that might mean the city has grown. Then again, it might just mean that new, more accurate data has appeared.

Moreover, nearly all of the data is estimated. Appropriate caution is therefore advised.

Spoilsports.

The biggest cities, by counting people

Anyway, let’s get to the fun bit. Here are the 10 largest cities in the world by population:

It’s pretty familiar stuff. The top 10 is dominated by Asian cities, with a strong showing from New York City. Tokyo is far in the lead, with Jakarta and Delhi coming up behind. For anyone who pays any attention to this stuff, there aren't at first glance any massive surprises.

We're not supposed to compare with last year's figures for all the reasons laid out above, but what the hell, here's the 2015 top 10:

There are two big differences worth noting. One is that only one Chinese city is now in the top 10, down from three last year. (Beijing and Guangzhou are now ranked 11th and 13th.) All three have seen their populations revised downwards: this seems to the result of previous over-estimates, rather than mass evacuations.

The other noteworthy trend is the sudden appearance in the top 10 of Mumbai, with nearly 23m people. Last year, it ranked 13th with 17.7m. In a section headed "Revised data: highlights", the report notes:

The Mumbai built-up urban area has been expanded to incorporate the Bhiwandi, Kalyan and Vasai-Virar urban areas.

In other words, it isn't that a population the size of Madrid has moved to Mumbai over the last year. Rather, it's become clearer that the megacity has expanded to swallow surrounding areas.

You can see why ranking cities is a complicated business.

The biggest cities, by measuring land

As noted, most of the biggest cities in the world by population are in Asia. Most of the biggest cities in the world by physical size are, well, somewhere else.

Suddenly, with the single exception of Tokyo, Asia doesn’t even feature. Eight out of 10 are in the US. Atlanta has an estimated 5.1m residents, so measured by population it’s the 79th largest city in the world. Measured by land area, though, it ranks fourth.


I guess this is what happens when you build your cities around the car.

Incidentally, the report estimates Atlanta's population density to be 700 people per km2. The comparable figure for Dhaka in Bangladesh – 16.2m people, the 16th largest city in the world - is 44,100.

Dhaka is 63 times more crowded than Atlanta.

All the megacities

One more chart: this is the top 36 by population.

The reason we've stopped at that arbitrary point is not to get London into the rankings (well, not only for that reason). It's because the common definition of megacity is that with a population over 10m.

This is all of them. We've colour coded them by continent:

That's three each in North America, South America, Europe and Africa.

But the remaining 24 – two thirds of all the world's megacities – are in Asia. Five of them are in China alone.

Here, because we love you, is the data used in that graph. Enjoy.



Rank City Population
1 Tokyo-Yokohama 37,750,000
2 Jakarta 31,320,000
3 Delhi 25,735,000
4 Seoul-Incheon 23,575,000
5 Manila 22,930,000
6 Mumbai 22,885,000
7 Karachi 22,825,000
8 Shanghai 22,685,000
9 New York City 20,685,000
10 Sao Paulo 20,605,000
11 Beijing 20,390,000
12 MexicoCity 20,230,000
13 Guangzhou-Foshan 18,760,000
14 Osaka-Kobe-Kyoto 16,985,000
15 Moscow 16,570,000
16 Dhaka 16,235,000
17 Cairo 15,910,000
18 Bangkok 15,315,000
19 Los Angeles 15,135,000
20 Kolkata 14,810,000
21 Buenos Aires 14,280,000
22 Tehran 13,670,000
23 Istanbul 13,520,000
24 Lagos 12,830,000
25 Shenzhen 12,240,000
26 Rio de Janeiro 11,815,000
27 Kinshasa 11,380,000
28 Tianjin 11,260,000
29 Lima 10,950,000
30 Paris 10,870,000
31 Chengdu 10,680,000
32 Lahore 10,355,000
33 London 10,350,000
34 Bangalore 10,165,000
35 Ho Chi Minh City 10,075,000
36 Nagoya 10,035,000

 

And if you want more of this stuff, here’s our report on the 2015 edition of the Demographia World Urban Areas Atlas.

Jonn Elledge is the editor of CityMetric. He is on Twitter, far too much, as @jonnelledge.

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