Traffic Technology

“Congestion pricing” models capture the attention of state and local governments from Seattle to New York.

What’s it worth to citizens to have a smooth commute to work? Minnesotans motoring along I-35W between downtown Minneapolis and the suburbs may soon be asked to pay as much as $8 — or as little as 25 cents — for the privilege.

The Minnesota state legislature is now considering funding a pricing model that creates dynamic tolls that change according to demand: The higher the demand, the higher the price. The project, which mimics the dynamic tolls in place for two years along the Minnesota stretch of I-394, is one of five federally funded projects that seek to reduce urban pollution and traffic with so-called value-pricing or congestion-pricing systems. Other cities include New York, Miami, Seattle and San Francisco.

The proposed projects would use different technologies, but they would have two things in common: automation and high-speed communication. From high-resolution video cameras to back-office servers that can change traffic lights and toll prices on the fly, each project requires massive amounts of data to be collected, transmitted, analyzed and acted upon in the blink of an eye.

Key Components

“Our internally developed software, called Intelligent Road Information System or IRIS, running on fiber-optic lines, is at the heart of our system,” says Bernie Arseneau, Minnesota’s state traffic engineer.

Minnesota collects data using a system of more than 4,000 devices, known as loop detectors, which register information about traffic volume. That system reports back to the state’s Regional Transportation Management Center (RTMC) in Roseville, Minn., every 30 seconds over the fiber-optic lines, says Arseneau. There, quad-core servers running IRIS crunch the data and — every three minutes — send updated toll prices to electronic signs at the entrance of the toll roads. Motorists who wish to use the dynamically priced express lanes — what transportation planners call HOT, for high-occupancy toll — must subscribe to the states MnPASS electronic-payment program that uses in-car RFID transponders to detect toll-road usage.

After some initial glitches in 2005, Minnesota’s HOT lanes have been a hit. They now carry one-third more drivers during peak periods. Similar success has been recorded on HOT lane projects on San Diego’s I-15, Denver’s I-25 and California’s State Route 91.

London, which became one of the first cities to try congestion-pricing systems, uses high-resolution video to capture license plate numbers, which are then entered into a database and matched against subscribers to its congestion-pricing model. Recently the city announced plans to add Dedicated Short Range Communications (DSRC) transponders like those used on many U.S. highways. Since 2004, the city has tested Wi-Fi, cellular and satellite-based global positioning system technology. Each has had mixed results.

In all cases, everything hinges on the back-end computing, says Rizwan Khaliq, global business executive for IBM’s Digital Communities initiative. “If the data can’t be validated and analyzed, it doesn’t matter what data you’re collecting on the front end,” he says. IBM recently won several consulting contracts to design and operate intelligent transportation systems in Brisbane, Australia; London; and Stockholm, Sweden.

“The other piece that is key is the back-haul network,” says Khaliq. “Especially if you’re using video, you have to have a broadband connection, whether it’s WiMax, a Wi-Fi mesh, or a traditional fiber-optic network.” WiMax offers data-transmission speeds of up to 12 megabits per second on licensed wireless frequencies; Wi-Fi transmits at up to 54Mbps.

For its part, Minnesota’s Department of Transportation is sticking with fiber-optic lines, though it will shortly be migrating from SONET-based fiber lines to Ethernet-over-fiber, according to Terry Haukom, Intelligent Transportation System architect for the state. “Wireless communication for us works great in limited cases, like at construction sites. But wireless technology requires a lot higher maintenance. We have over 400 miles of serviced roads. If we switched to wireless, we’d need three times as many maintenance workers.”

Whatever method state and local governments use, congestion-pricing plans will spread, says Patrick DeCorla-Souza, program manager for the Federal Highway Administration’s Urban Partnership Program, which is working with Minnesota on its projects. “Within five years I envision current technology, DSRC or video tolling where you don’t actually need a transponder, as in London [where] you simply get charged by your license plate. In 10 years I see entire freeway systems being priced.”

Apr 25 2008