Transportation

Weighing trucks in motion: good for roads, good for safety

Truck traffic is increasing, making it even more urgent to keep overweight vehicles off roads and bridges. “Overloaded trucks are more prone to accidents because of longer braking distances and a heightened risk of rollovers and blown tires,” explains Ingrid Sagorz, product manager at Kistler Group. Heavy loads also reduce pavement lifespan and accelerate bridge fatigue. In fact, a three-axle truck weighing 30 tons can cause as much pavement damage as 7,500 cars.

Traditionally, inspectors select which trucks to weigh based on their appearance and the operator’s record. But some violators evade detection, compliant drivers are inconvenienced, and long queues at the weigh station disrupt traffic. A more efficient approach is to weigh every truck as it travels over the highway using sensors embedded in the pavement. Switzerland’s Kistler Group is a world leader in Weigh in Motion (WIM) solutions. The company’s highly accurate quartz sensors capture weight and tire condition as the vehicle moves at any speed, even if the driver changes lanes while crossing the measurement area. Trucks with a gross or axle weight that exceeds the legal limit are directed to pull into the weigh station or are fined directly. “Allowing compliant trucks to continue their journey without stopping for a weight check is safer, speeds up the supply chain, and reduces fuel consumption,” Sagorz says.

Accurately calculating weight in motion

To reliably identify overloaded trucks, every element of the WIM measuring chain—sensor, network, and software—needs to be fast and accurate. Kistler’s flagship KiTraffic Digital solution, which includes Cisco Industrial Ethernet Rugged Series Switches, has been awarded the OIML R134 certificate for the highest accuracy class, F5, by the Swiss Federal Institute of Metrology (METAS).

Here's how it works. Kistler’s weight sensors are installed flush with the pavement. A typical installation has four sensors per lane—20 sensors for a 5-lane highway. Off to the side of the highway, a roadside cabinet houses a pre-wired panel containing one or two 28-port Cisco Catalyst IE9300 Rugged Series Switches, an industrial PC running Kistler’s software, and a router used for remote access. The Catalyst IE9300 switches provide power over ethernet (PoE) to all sensors, which transmit data the software uses to calculate vehicle weight, type, speed, position, and lane. Some traffic authorities use KiTraffic Digital to pre-select overweight trucks for static weighing. Others use it for direct enforcement, sending WIM data in real-time to traffic data centers for further processing and fining or other regulatory actions.

Cisco switches help Kistler measure total vehicle weight and axle loads with accuracy and precision, even when vehicles are zipping along at highway speeds and changing lanes. “Traffic authorities can trust the accuracy of the WIM measurements from KiTraffic Digital because the Precision Time Protocol (PTP) in Cisco industrial switches precisely synchronizes all sensors,” Sagorz says. “Since PTP is built into the Cisco switch, there’s no need for an external PTP time source or additional synchronization hardware—an important advantage in space-constrained roadside cabinets.” Enforceable penalties give trucking companies an extra incentive to comply with weight regulations designed to keep highways and bridges safe and in good repair.

Transmitting information when it’s most useful

When an overloaded truck is approaching, inspectors need enough advance warning to direct the driver to a weigh station. An alert that arrives even a fraction of a second too late can result in an overloaded truck continuing on its way without weighing, stressing roadways and bridges. “With their low latency, Cisco switches can quickly transmit the vast volumes of data our sensors generate in near real-time, in time for inspectors to take action,” Sagorz says.

Standing up to harsh outdoor conditions for many years

Besides moving data at the speed needed for WIM, Cisco industrial switches conserve space in cramped roadside cabinets. “By combining switching, synchronization, and PoE in one device, Cisco industrial switches reduce cabinet clutter, simplify installation, and improve overall reliability,” says Sagorz. “They’re also rugged, operating reliably in freezing Northern European winters and sweltering Middle Eastern summers.”

The long life of Cisco industrial switches also appeals to Kistler’s customers. Unlike enterprise network devices, industrial switches used in transportation infrastructure are expected to operate reliably for 10 years or more. “The long lifespan of Cisco industrial switches makes them a good match for our sensors, which often outlast the pavement where they’re installed," Sagorz says.

As truckers keep on trucking, Kistler’s KiTraffic Digital solution, powered by Cisco industrial switches, keeps on weighing, helping to make the world’s roads and bridges safer.

Advanced Weigh in Motion solutions from Kistler reliably detect overloaded vehicles and help to protect roads and bridges.