We've been talking up urban transport all week hereabouts, so I figured I'd finish it with a Friday look at highways in the city.

Since the 1940s, the one-size-fits-all solution to urban traffic problems has been road construction, and it's a solution that comes only in two sizes: big and bigger. Build 'em wider, add some lanes, raise 'em to the sky and up the speed limit. Keep at it long enough, and eventually there'll be enough room in the city for all those fast-moving cars.  

It's a political no-brainer. Traffic woes top the list of city-dweller complaints in elections at every level, and what better response could a politician give than to promise more roads, better roads, expressways, highways, express highways and superhighways and freeways and parkways? If you've got two cars and a single garage, what do you do, Joe Homeowner? You build a wider garage. Same deal with a road, right? It's just common sense.

It's also dead wrong.

Study after study for a generation now has demonstrated that more and wider highways just create more traffic. Years ago, New Urbanism founding father Andres Duany pointed out that for every 10 percent increase in roadway capacity, you wound up with a 9 percent jump in traffic volume. A British study found that the main impact of an expensive showpiece bypass-building scheme was a 50 percent increase in total traffic. And here's the main takeaway from a recent investigation that looked at road construction in 70 metro areas over 15 years:   

Metro areas that invested heavily in road capacity expansion fared no better in easing congestion than metro areas that did not. Trends in congestion show that areas that exhibited greater growth in lane capacity spent roughly $22 billion more on road construction than those that didn’t, yet ended up with slightly higher congestion costs per person, wasted fuel, and travel delay. 
This is a conclusion worth repeating: spending lots more on roads increased the toll exacted by congestion. Building more highways intensifies the urban traffic mess.

Not only do highways fail on their own promise of smoother commutes, they ruin the cityscape around them. That's why the most promising trend in urban traffic management is the destruction of highways — particularly the "grade-separated highways" so beloved by the previous generation of urban transportation departments.  

A particularly dramatic case in point comes to us from traffic-clogged Seoul, Korea, where a few years ago a handful of "crazy" visionaries in the transport department somehow managed to sell a new mayor on the demolition of an elevated downtown highway. Fast-forward to today: the highway's gone, a formerly paved-over river has been rehabilitated, the resulting green space is a source of urban pride, and — wait for it — motor vehicle travel times have actually improved in the neighborhood of the old highway.

Similar results have emerged from American highway demolitions. Alas, tearing down highways is a very hard sell politically, so the best U.S. cases in point were precipitated by natural disasters — the collapse of the West Side Highway in New York in 1973 and the demolition of San Francisco's Embarcadero Freeway after it was heavily damaged in the 1989 earthquake.

Here's an excellent video summary of the impact of both demolitions on traffic from the never-not-fascinating folks at Streetfilms:

 

Did you catch what former New York traffic commissioner Sam Schwartz said there about the West Side collapse? "The traffic was able to take different paths. Things didn't get worse on all the other routes that had to pick up the slack."  

This should, by rights, become the new common sense in urban traffic management: The cars will find a way, and if they don't then people will use other forms of transportation. And the net impact on the livability of the city will be positive in every case. The only good downtown highway is a demolished downtown highway.  

To sing the praises of destruction in explosive 140-character bursts, follow me on Twitter: @theturner.

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