May 1, 2010 12:00 PM, By Merrill Douglas

GPS probes supply travel-time data that help drivers find more-efficient routes

On your usual route to work, vehicles are crawling at 20 mph. On a parallel road, though, drivers are zipping along. Wouldn't it be nice to know all that before you get stuck in traffic?

These days, motorists in a long slice of the East Coast can base their driving decisions on real-time knowledge of local traffic conditions, thanks to a multi-state intelligent transportation systems (ITS) initiative. The Vehicle Probe Project uses data from global positioning system (GPS) devices installed on vehicles to calculate traffic speeds on Interstate 95 and nearby roadways. The pilot project covers a region that stretches from New Jersey to South Carolina.

The project's sponsor is the I-95 Corridor Coalition, a partnership of transportation agencies, toll authorities and other organizations in states extending from Maine to Florida.

Transportation agencies have used in-pavement sensors, roadside radar, cameras and other instruments for many years to monitor traffic. Those technologies are good at detecting major slowdowns, but not at measuring ordinary traffic flow, said Bill Stoeckert, information and payment service coordinator for the I-95 Corridor Coalition. "They haven't been proven to be a very useful tool for providing travel times."

Nor do they come cheaply. "You have to go to the expense of designing and building and communicating with them, and then you also have to maintain those sensors," said Rick Dye, systems administrator for the Coordinated Highways Action Response Team (CHART) program at the Maryland State Highway Administration (MSHA).

Federal, state and local transportation officials want to do more than merely report when an accident that forces traffic to a near-standstill occurs, Stoeckert said. They also want to tell drivers, under any conditions, how long it will take to drive from Point A to Point B.

The vehicle-probe technology gives coalition members that ability. "It's mainly to supplement existing detection systems that they may already have, or provide additional detection and speed information that they don't have on certain segments of their highways," Stoeckert said.

To obtain the travel-time data, the coalition has contracted with Inrix, a Kirkland, Wash.-based vendor of traffic information. Inrix's customers include commercial traffic-information services, government agencies and consumers.

Much of the data that Inrix employs to calculate traffic speeds comes from GPS devices installed on tractor-trailers, delivery vans, taxis, utility trucks and other fleet vehicles.

Inrix forms agreements with companies that sell automatic vehicle location (AVL) and fleet-management services to fleet owners, or it sometimes contracts with the owners themselves. As these companies collect data on location, speed and heading from the vehicles, they share that information with Inrix. The company also collects GPS data from other sources, including consumers who use its traffic-information application for the iPhone and, through an agreement with Ford, the SYNC onboard navigation system.

Using proprietary technology, Inrix processes the aggregated, anonymous data to calculate traffic speeds on specific road segments.

In some areas, Inrix adds data from transportation departments' own roadway sensors to the mix. "Then we fill in all the gaps on the roads where sensors are supposed to be operating but they're not, or where they don't have sensors, period, to give a complete, integrated picture, updated every minute," said Rick Schuman, Inrix's vice president, public sector.

To calculate travel times for the I-95 Corridor Coalition, Inrix draws upon a broad, constantly changing mix of sources, Schuman said. "We have probably three to four times the amount of raw data going into this system than we did when we started the project a little less than two years ago." Inrix also has improved its processing methodology, producing ever-more-accurate speed calculations, he said.

Since July 2008, the coalition has been purchasing traffic-speed data from Inrix for I-95 and adjoining highways in six states — 1,500 highway miles in all — running from New Jersey to North Carolina. New Jersey and North Carolina each added coverage on all limited-access highways within their borders. South Carolina joined the pilot in August 2009.

"As a result of North Carolina, New Jersey and South Carolina using the contract provisions for expansion, the total coverage is now 4,700 miles," Stoeckert said. On top of that, Inrix is donating coverage on 1,000 miles of arterial roads, he said.

Funding for the Vehicle Probe Project comes from the program budget of the Coalition, which receives much of its support from the Federal Highway Administration (FHWA).

To make sure that the probe data is accurate, researchers at the University of Maryland have been conducting validation tests, using Bluetooth technology to measure travel times and comparing those with Inrix's reported times.

The researchers use pairs of roadside detectors to capture signals from Bluetooth-equipped devices, such as hands-free cell phones, in cars as they pass. Those signals include anonymous Machine Access Control (MAC) addresses. The time it takes a MAC-address signal to pass from one detector to the next is the travel time on that section of roadway.

"After the data started coming in, in July of 2008, they did a validation of the whole system," Stoeckert said. Measurements showed that the data was meeting the contract requirements. Since then, researchers have conducted monthly validations on selected highway segments. The validation data is a component of the payment formula that the coalition established with Inrix, he added.

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