A microscopic analysis can simulate when a driver changes lanes, speeds-up, slows down, how close do they follow the car in front of them, and the speed at which they follow, among other variables. It can update measurements every one-tenth of a second, said Hummer.
It is expensive software to run and is only used on big projects — such as lane closures. The economic cost of the New Jersey lane closures more than justifies its use, Hummer says.
Eventually these models will get sophisticated enough to be able simulate "really odd driver behaviors" that can create accidents, and to predict collisions before they occur, Hummer expects. Collisions are relatively rare and are tough to model, but Hummer is hopeful that improvements in computing power and the underlying logic can solve this problem.
Lorenzo Rotoli, an engineer and vice president at Fisher Associates, a civil engineering firm in New York that works on roads, bridges and signal systems, uses the high-end PTV Vissim software for traffic modeling. He said the software can reproduce real-world traffic conditions.
"I would be pretty confident that if we knew exactly which lanes are closed we could replicate that, and it would show exactly how bad the backups are going to be," said Rotoli. He tempers his observations by noting that he has no insight in the Port Authority situation, but said "I can't imagine their particular scenario was so unique and so different that the higher end software (tools) couldn't have handled it," he said.
Traffic data for computer models can be collected in several ways. Tubes can be installed that register a pulse of air when a car passes over. Some sensors can be screwed or nailed into in a roadbed. Installing these systems may involve some short-term road closing. Also, people could be also be deployed to count vehicles.
On busy roadways, though, engineers are likely to use camera video detection with software that can count vehicles. That's the least intrusive method, and the documents released last week suggest that such a video camera system in installed on the George Washington Bridge.
Once engineers define what it is they are measuring, the data is gathered, and then an existing condition model is created. The model is calibrated against existing conditions, and from there the simulations are run to assess the impact of something like a lane closure or a road construction project, said Rotoli.
The computer models, which can show animated vehicles, bicyclists and pedestrians, can also be used to inform the public and officials about the impact of a road project.
New Jersey's alleged study increased risks to motorist as well as delayed their travels. "When there are delays people get frustrated they drive more aggressively and accidents happen, "said Rotoli.
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