ices is the cost of sending electronic signals between them and the transportation center that is doing the monitoring. Normally, controller boxes transmit their data very frequently. Some do so as often as once every twenty seconds.
"When the number of controller boxes in use around the country was small, the communication costs were small, but now that the numbers are increasing, so are the bills," Coifman said. He wants to help states leverage those detector stations and keep costs down.
He and former graduate student Ramachandran Mallika wrote software that enabled the controller boxes to detect traffic incidents and get important messages back to the traffic control center using a fraction of the bandwidth that was previously required.
In the October 2007 issue of the journal Transportation Research Part A, they report that their software achieved better than 90 percent accuracy in reporting traffic conditions at the interchange between two busy Columbus, Ohio interstates -- using up to 200 times fewer signals than before.
Instead of sending all of the data all of the time, the new software infers road conditions based on traffic patterns. It determines whether conditions are critical enough for an alert to be sent to a state transportation authority. Otherwise, it sits quietly and leaves the communication channel free.
For example, if traffic stalls at an interchange, the controller box could alert authorities that it suspects an accident. If conditions are fine, no data are sent.
"With this approach, no news is good news," Coifman said.
The approach is more efficient, because the controller boxes only send signals to the control center when absolutely necessary, which reduces communications costs. The transportation authorities would only need to electronically "ping" a quiet station once in a while, to make sure it was still working.
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