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Really? Cones for a traffic study?

We should have been suspicious when New Jersey Gov. Chris Christie first explained the closed lanes on the George Washington Bridge as being necessitated by a traffic study. 

Fact is, traffic planners rarely — if ever — shut down lanes to perform traffic studies these days. "In general we don't disrupt traffic unless there is an engineering reason to do so, whether that is construction or signal timing adjustments or things like that," said Doug McClanahan, traffic analyst with the Washington State Department of Transportation. "Our aim is to not get in the way of traffic at all. All 50 states are probably like that."

To do their traffic studies without getting in the way of drivers, McClanahan and his colleagues turn to traffic microsimulation software, such as Corsim and VISSIM. Corsim is a Windows-based traffic simulation and analysis program developed by the Center for Microcomputers in Transportation (McTrans), which was established by the Federal Highway Administration. VISSIM, also a Windows application, was developed by PTV Planung Transport Verkehr AG in Karlsruhe, Germany. (The acronym is for German words that translate as "Traffic in cities - simulation model.")

The first step in a traffic study, says McClanahan, is to collect data on existing patterns. That, too, can be accomplished without disrupting transportation. "There are a couple places where we get our data," said McClanahan. "If it's operational – that is, if it's today's data – we can get that through mechanical counters, individual human beings who count, in-road monitors and video cameras." 

Next, the data is plugged into a microsim program, which analyzes driver behavior and which allows an analyst to set parameters and change variables such as, yes, the number of lanes available for the traffic or the timing of traffic lights on a stretch of road.

"We have analytical models and we have simulation-type models," said McClanahan. "When we apply those, we can generally understand what's going to happen if we make a geometric or signal timing change." He adds that this is a relatively recent capability. "We've been able to do static models for 30 years," he noted. "But microsimulation is something we've really only gotten into in the last decade or so."

As for the effect of closing lanes on a bridge? "We can simulate that, given time and budget," McClanahan said. "If the issue is emergent and we don't have time to do a simulation using computers, we would have to look to other methods."

Posted by Patrick Marshall on Jan 21, 2014 at 12:20 PM


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