When upgrading the weigh-in-motion scales and software last month, the Mackinac Bridge Authority (MBA) worked with the Michigan State Police Motor Carrier Division, equipment provider D.C. Martin and Son Scales of Grand Rapids, and equipment manufacturer Metler Toledo of Columbus, Ohio. Standing behind the weigh-in-motion scale are (from left) electronics technician Brent Garries of the MBA, President Coby Martin of DC Martin and Son Scales, Michigan State Police Lt. Rodney Bloss, Senior Project Manager Tom Kimmet of Metler Toledo, and police officers stationed at the bridge, Craig Therrian and Dan Litzner. (Photograph courtesy of Mackinac Bridge Authority) Accurate screening of trucks and other commercial vehicles was set in place last month at the Mackinac Bridge as 13-year-old weigh-inmotion scales were rebuilt and the system's computer software was upgraded. The changes, say bridge and law enforcement officials, will help protect the infrastructure of the bridge and nearby roads.

The bridge was designed for three-axle trucks weighing a maximum 72,000 pounds, said Bob Sweeney, executive secretary of the Mackinac Bridge Authority. Heavier loads are allowed on Michigan roadways, so an analysis of the design of the bridge was performed and it was determined that trucks up to 144,000 pounds, with restrictions, could cross the bridge.

Those trucks require 500-foot spacing and must travel at lower speeds, which is essential to prevent the bridge from being damaged from these heavier loads, he said.

Regulations for trucks are enforced from the toll plaza in St. Ignace to the Jamet Street exit in Mackinaw City and include a maximum speed limit of 20 miles per hour, using the right lane with no passing, 500-foot spacing and no tailgating, and use of four-way flashers. Trucks with a gross load of more than 40 tons must request an escort before crossing the bridge, and the maximum allowable vehicle weight is 72 tons (144,000 pounds).

Overweight trucks cause the greatest damage to the bridge and that results in higher maintenance costs, said Mike Litzner, chief financial officer of the Authority.

"That's why we want to keep weights to what the bridge was designed for," he said, "as overweight trucks will increase the wear and tear on the bridge."

In 2007, he said, 285,336 trucks crossed the bridge.

Mr. Litzner worked on the upgrades with MBA electronics technician Brent Garries, who managed the work on the project.

The new system, said Mr. Garries, is more accurate.

The bridge's project was done in collaboration with the Michigan State Police Motor Carrier Division, which is charged with weight enforcement on Michigan roadways, including the bridge.

A narrow plate in the roadbed just north and south of the toll booth plaza weighs vehicles as they move toward the toll booths. Work at the site in July included installing new fiber optic cables.

The electronic data gathered as a truck passes over the scale is transmitted through the cables to a computer, and is displayed on a monitor in the operations room at the building just east of the toll booths.

The information is recorded and includes the truck identification, time, weight of the truck and axles, and axle configuration. The information also is used by the Michigan Department of Transportation (MDOT) to track traffic patterns.

As a truck passes over a scale, if the overall truck or an axle weight is over the limit, an alarm is triggered in the operations room. Bridge staff then contact the state police. The MBA can hold the truck up to two hours, until a State Police Motor Carrier officer arrives at the bridge. The bridge authority can pull the carrier's bridge permit, if it chooses, and if the carrier has one.

Michigan State Police covers traffic enforcement on the bridge, and since 2005, police began meeting regularly with highway department officials to collaborate on strategies to improve commercial vehicle enforcement throughout Michigan. Their purpose was to protect highway infrastructure, promote highway security and safety, and enforce laws.

"One of our number one goals," said Lieutenant Rodney Bloss of Gaylord, "is to keep that bridge functioning and viable. I can't even imagine the economic toll it would take on both sides of the bridge if it were to be damaged. I call it my bridge. I'm protecting my bridge."

Lt. Bloss is the district commanding officer for the traffic safety division of the Michigan State Police. He is responsible for 19 counties in the Lower Peninsula and the entire Upper Peninsula, including both the Mackinac and International bridges. A team of 23 state police officers, sergeants, and inspectors reports to him. Locally, officers Dan Litzner and Craig Therrian are stationed at the bridge.

At the bridge, Lt. Bloss said, an overweight southbound truck would be stopped by an officer before it crossed the span. A fine would be issued and the trucking company would be required to off-load the amount of weight the truck is overweight, before it would be allowed to leave.

Fines are graduated and range from 3¢ a pound to up to 20¢ a pound. For example, a fine for a truck at 10,000 pounds over the weight limit, fitting a 20¢-perpound penalty, would be issued a $2,000 fine.

The fines are issued by the state police and, by state law, are given to libraries within the county where the fine is issued.

An overweight northbound truck has already crossed the bridge when it reaches the weighin motion sales. The truck also is fined and must off-load its cargo to meet legal weight limits.

Weigh-in-motion scales, said Lt. Bloss, also are stationed south of the bridge on US-127, US-131, and on I-75, and along US-2 in the Upper Peninsula. These scales relay information to laptop computers in patrol vehicles. An officer can be up to one mile away from a scale and still receive the information on the computer in the patrol car.

"If you're legal and you run down the road, who cares? It's that guy that's not running legal," said Lt. Bloss, "the guy damaging the roadways — we won't sacrifice public safety nor the roads for their convenience. So the best thing they can do is run legal weights."

Within five years, weigh-inmotion scales also will be constructed at the International Bridge at Sault Ste. Marie. A fixed scale now is used at that structure.