I joined the stable again over at the New York Times’ Room for Debate, this time on the idea of full highway shutdowns.

Just for historical curiosity, here’s my original, somewhat more fanciful (but contextual) submission:

It’s perhaps appropriate that the town that produced Michael Bay should summon such a bombastic bout of overblown apocalyptic fury as the forthcoming “carmaggedon.” Given the life-support functions of the 405 in the L.A. region’s transportation monoculture, perhaps the hype is warranted, but the truth is, highways are closed all the time, and there’s been much study and practice into how to do it most effectively.

The perturbed driver may be asking, ‘why do they have to close the whole thing down? Why can’t they just do it a lane at a time?’ And indeed, any number of strategies have been tried to mitigate traffic impacts during construction, from nocturnal work crews (which has been found to add 6% to the base price of a project) to various incentive plans for road contractors.

But as research by the Federal Highway Administration has shown, closing down a highway entirely means the job gets done, on average, 63 to 95 percent faster than projects that tried to maintain a semblance of traditional traffic. Why? No traffic means no interference from drivers, no work-zone crashes (in 2007, for example, 835 people were killed in work zone crashes) or other bad behavior, not to mention that the trucks hauling materials and workers don’t have to sit in the same congestion as everyone else as they go back and forth.

The secret to making this happen, as is happening in Los Angeles, is to enact a comprehensive “Traffic Management Plan,” with careful study of alternate routes and “network effects.” Implicit in this is to issue a prediction of Nostradamusian direness; to do for weekend driving what Jaws did for ocean swimming (“just when you thought it was safe to go to Santa Monica”).

This reason this generally works is that in any road system, there is a certain amount of elasticity; not every driver on that road has to be there at that time. There may be another route, another mode of travel. Or they just stay home. When highway segments are taken out because of disaster (as in the Minneapolis I-35 W bridge collapse, or the collapse of Manhattan’s West Side Highway) the surrounding roads do not automatically filled up with all the diverted drivers; rather, some traffic “disappears.” To quote two of the main findings of a report analyzing any number of road closures, planned or otherwise, by transport researcher Phil Goodwin and colleagues: “When roadspace for cars is reallocated, traffic problems are usually far less serious than predicted” and “Traffic reduction is partly explained by recognizing that people react to a change in road conditions in much more complex ways than has traditionally been assumed in traffic models.”

When Los Angeles partially closed the 710 expressway for eight weekends, it was able to reduce traffic by 37%. Interestingly, though, traffic was lowest through the work zones the first weekend, and then grew gradually on each successive weekend, as L.A. drivers, in a kind of city-wide learning curve, began testing the drive. In the case of the 405 closure, of course, drivers won’t have that option. There’s no knowing how bad or how good it’s going to be, until you’re in it.

This entry was posted on Friday, July 8th, 2011 at 6:46 am and is filed under Cars, Cities, Commuting, Congestion, Traffic Engineering, Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.