Scaling it down

News November 22, 2000
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Sometimes it's hard to get trucks to stand on a scale

Sometimes it's hard to get trucks to stand on a scale.

Using traditional methods usually creates long lines at weigh stations, making it difficult for truckers keeping a tight schedule.

But technology is taking the pounds off in terms of time, as weigh-in-motion scales make the checks swift and relatively inexpensive.

The Minnesota Department of Transportation (MnDOT) recently had the electronic monitoring system installed at its St. Croix weigh station on eastbound I-94 near Hudson, Wis. Minnesota is among eight states chosen to pilot Commercial Vehicle Information Systems and Networks (CVISN) development, receiving a total of $7 million in federal, state and private funding to develop the system.

The system automatically checks the vehicle's size and weight, identifies its operator and verfies its safety performance history and other credentials.

"Based on the experience we have (at St. Croix) we would hope to expand it to other facilities," CVISN Project Manager, MnDOT Motor Carrier Services, Chris Conway told ROADS & BRIDGES.

Hopefully the idea will catch on fast. Weigh stations are crumbling across the country due to the cost to run such an operation and the inability to find trained workers. Weigh-in-motion scales would eliminate such problems.

Electronic sensing equipment has been installed on the ramp at St. Croix. Truckers drive over the scale without stopping and pass a height sensor. Vehicle identification is picked up by a radio receiver on the side of the road and a picture of the license plate is taken. Due to a short ramp, drivers must slow down to 25 mph at St. Croix, but can travel as fast as 60 mph at other stations. The decision on whether or not a truck can return to the road is made via computer and takes no longer than a couple seconds.

"The only time an operator gets involved is after the system has made a decision that this vehicle should be looked at closer," said Conway.

It's estimated that time spent away from the highway at St. Croix is less than a minute. Using traditional methods weighing could take 15-20 minutes if a line is stretched all the way back to the mainline.

"At the very best case scenario, with no traffic, it could be two or three minutes," said Conway.

Weigh-in-motion technology isn't exactly fresh. Some states have been implementing it for some time, but what has been recently developed is a mechanism to receive safety and credential data that's accurate and timely out of the weigh station facilities.

In the past, states have used a service that checks a carrier's credentials and safety at the time of application, giving them the green light for at least a year.

The significance at the St. Croix station is that it's linked into a North American-wide network of safety and credential data, keeping everything up to date.

"If we have information that a carrier has suddenly slipped into a bad safety status then we can give their vehicles a closer scrutiny," said Conway. "In the past we would never be able to do that kind of thing. It would take several months for that information to work its way through all the jurisdictions."

Parts of the weigh-in-motion system, however, is dependent upon an on-board transponder which isn't found on every truck. And Conway says there really is no way to check credentials or safety records without some type of on-board vehicle identification.

"Some states actually issue transponders to their carriers, but we've taken a low-key approach," noted Conway.

If a carrier does not have an on-board transponder the license plate readers can serve as a back up. An identification attempt could be made, but it isn't always successful. The variety of plates out on the road tends to confuse the system.

Conway hopes to one day see "virtual" weigh stations out on Minnesota roads. The virtual concept would allow readings to be made right on the highway. They're also exploring the idea of arming state troopers with on-board computer systems to make the necessary checks.

"We're also looking at mobile applications without necessarily any fixed equipment on the roadside. Not only would we have portable sensor equipment, but we would also have the ability to link up to the safety and credential database so the operators can make that check remotely," added Conway.

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