Does road construction really snarl up traffic?

How we get from here to there.
June 9 2009 6:21 PM

Men At Work

How much does road construction really snarl up traffic?

(Continued from Page 1)

One common response has been to shift almost entirely to nocturnal construction. (Rush-hour roadworks are a very rare sight these days.) On highways like the Connecticut Turnpike, which as a RAND report notes operates during peak hours at "close to 185 percent of its target capacity," most road construction happens between 8 p.m. and 6 a.m. While this means paying higher wages to workers (adding, according to one study, about 6 percent to the base cost of a lane improvement) and often extends the time it takes to complete projects, the other benefits—less congestion, fewer work-zone crashes, reduced emissions, etc.—on average seem to far outweigh the added costs. Another strategy has been to make the road crews themselves more efficient. So-called "cost-plus-time" bidding (or "A+B bidding" as it's known in the business) makes completion time an essential variable in the bid, while the even more effective "lane rental" strategy actually charges the contractor for the right to "occupy" a travel lane (a form of "congestion pricing," if you will) in increments as small as 15 minutes.

Perhaps the most radical but effective solution is known as the "full-road closure." This no doubt sounds apocalyptic (and a touch counterintuitive) to the commuter, but road agencies have gradually learned that shutting down one direction of travel or an entire highway—typically round-the-clock during several successive weekends but sometimes for longer—is faster than trying to complete road projects while active traffic whizzes by. No traffic means no work-zone crashes and less interference from drivers, and it also ensures that trucks hauling gravel and other material and equipment no longer have to sit in the same congestion as everyone else en route to the work site. A study by the Federal Highway Administration looking at six full-closure projects found time savings ranging from 63 percent to 95 percent versus projects that tried to maintain traditional traffic.

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Closing much or all of a highway requires extensive upfront planning—what's called the "Traffic Management Plan." Drivers have to be warned and given viable and signed alternate routes, and attention must be paid to the overall "network effects." For example, when Caltrans (California's DoT) repaired the I-710 (the Long Beach Freeway) over a set of eight 55-hour weekend partialclosures, it monitored suggested detours and other nearby routes for traffic impacts. * The agency found it was able to reduce traffic through the construction zone by some 37 percent, while traffic on nearby arterials, not surprisingly, increased; a certain number of drivers, meanwhile, were simply "no-shows," deciding the added hassle wasn't worth it. But Caltrans noticed an interesting pattern: Traffic through the congested work area was lowest the very first weekend but gradually grew over successive weekends, as a kind of "learning curve" set in and drivers tested varying strategies for getting around the detours.

So, a lesson for this summer may be: Drive through the construction you've been warned about when you first hear the warnings. After that, it's only going to get worse.

Correction, June 11, 2009: This piece initially referred to the Long Beach Freeway as the 701. It's the 710. (Return  to the corrected sentence.)

Tom Vanderbilt is author of Traffic: Why We Drive the Way We Do, now available in paperback. He is contributing editor to Artforum, Print, and I.D.; contributing writer to Design Observer; and has written for many publications, including Wired, the Wilson Quarterly, the New York Times Magazine, and the London Review of Books. He blogs at howwedrive.com and lives in Brooklyn, N.Y. You can follow him on Twitter at www.twitter.com/tomvanderbilt.

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