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Chris Christie’s traffic study excuse didn’t even make sense

At New Jersey Gov. Chris Christie's garment-rending press conference Thursday, the humble traffic study got its moment in the spotlight.

“I don’t know if this was a traffic study that morphed into a political vendetta or a political vendetta that morphed into a traffic study,” Christie said, claiming ignorance to explain why he didn't put the kibosh on the closure of two on-ramp lanes from Fort Lee to the George Washington Bridge -- choking off an essential connector from residential neighborhoods to jobs in Manhattan.

He's got something right: Traffic studies, which forecast the effect of new developments or changes in roadway configurations on the flow of vehicles, can sometimes be political documents. Usually, the consultants who prepare the studies are paid by the people building the project for which they're required, so they have every incentive to show the project won't have any noticeable impact.

In this case, however, the traffic study should never have been a viable excuse -- anybody who knows anything about them would realize that a traffic study could never turn a bridge into a parking lot, because traffic studies rarely involve actually doing anything to traffic.

Let's start with how you make a traffic study. Traffic engineers will assess the existing flow by counting cars, either manually (like with clipboards) or using more sophisticated surveying tools like cameras and meters (as my colleague Ashley Halsey III points out). Then they'll take standard calculations for what the proposed change would introduce, and plug them into formulas provided by the Institute of Transportation Engineers. It's a pretty automated procedure, with little impact on traffic.

"You might look at an existing facility, to see how can we improve operations of this facility," explains Rachel Weinberger, a principal with the transportation planning firm Nelson Nygaard. "But you wouldn't do it by closing down two out of three traffic lanes for days and days."

Why? Because transportation engineers already know that making cars merge into oncoming traffic, rather than giving them their own lanes -- what's known as a "weave" -- necessarily slows traffic down a lot. (Of course, for Christie's vengeful underlings, that seems to have been the point.)

Sure, sometimes you might have to interfere with traffic in order to conduct a simulation. But before that happens, most jurisdictions require engineers to complete a "maintenance and preservation of traffic" plan, which typically goes through a public review process. At the end, you have a fairly non-invasive operation. "You'd go at 2 a.m., and put those rubber tube counters down, so you could count how many vehicles are coming," Weinberger says. "Sometimes we have to do surveying. So you might close a shoulder or a lane to protect the surveyors so they don't get run over by cars. But you would do one lane, not two out of three. And you would do it one day a week."

Only very occasionally will jurisdictions actually shut down whole sections of traffic on a trial basis -- when New York was deciding whether to make Times Square into a pedestrian plaza, former Mayor Michael Bloomberg started with an eight-month trial before deciding to make it permanent. "So but again, they would've done the simulation first," Weinberger says. "They would've said to the people who are nervous about it, 'we really believe that this is going to work, so we'll try it for six months and then we'll reassess.'"

As it happens, New Jersey did end up studying the effect of the lane closures on George Washington Bridge traffic, and found it to be a disaster for local people -- but better for further-out suburban commuters coming through the mainline toll lanes. That's something that cities often deal with, since suburbs tend to be over-represented in the metropolitan planning organizations that make transportation decisions on a region-wide basis.

In this case, obviously, different forces were at play.