The ‘weight’ is over for legal-for-trade weigh in motion

By |  November 8, 2021

Draft dilemmas

Prior to NCWM’s decision, scale manufacturers lobbied for multi-draft WIM scales to become legal for trade.

The holdup on that happening resides in the tolerances allowed by NCWM and the National Type Evaluation Program (NTEP), which certifies that scales meet strict marks.

Currently, static scales must be able to measure the weight of a truck within 0.1 percent for the first 30 days of operation (acceptance tolerance). After that, it can be within 0.2 percent (maintenance tolerance) from there on out, until it needs to be recertified. In other words, if a truck and the materials in it weigh 1,000 pounds, the scale must be able weigh that truck within 0.1 percent (1 pound) or 0.2 percent (2 pounds) on the high or low side.

Full-length, single-draft WIM scales will be held to the same tolerances as static scales under NCWM code and therefore will be legal for trade, but multi-draft WIM scales, are not coded for legal-for-trade in Handbook 44..

“Our first [WIM] scale would consistently hold 0.3 percent on average, and it can hold 0.2 now,” Fryburger says. “Is that a big change? In our world, it’s a big change, but it’s not massive. If you look at a group of weighments … repeatability wise, we can hold within 0.2 percent and do it pretty consistently.”

Joe Grell, vice president of heavy capacity products at Rice Lake Weighing Systems, says an added issue is the size and cost associated with installing a full-length scale and making it WIM accessible.

“A multi-draft scale set up for non-legal for trade can have a dirt approach, and the scale is typically 30 in. long and 10 ft. wide with dirt approaches on either side,” Grell says. “So, they’re relatively inexpensive. You can probably put one in for well under $40,000 today. A 70-ft. [single-draft] truck scale is probably $120,000 to $130,000.”

Imminent implementation

Several companies, including Cardinal Scale, Rice Lake and Mettler Toledo, previously began preparing for a time when WIM scales become legal for trade. These manufacturers are ready to sell full-length scales that are capable of in-motion weighing.

“This has been worked on for the last five years,” Grell says. “Along the way, a couple companies – Rice Lake being one and Mettler Toledo being another – did extensive testing on turning an existing static scale into an in-motion scale.

“We are going to be one of the first companies to go through the NTEP test [with the new in-motion scale],” Grell adds. “We’re ready [and] Mettler Toledo is ready. That’s reality in 2022.”

Still, just because WIM scales provide certain benefits doesn’t mean static scales will go by the wayside. This is both because the WIM scales that are becoming legal for trade need to be single-draft static scales to begin with – and that the additions needed to utilize weigh in motion will come at a steep price.

“I’m not sure in-motion, legal-for-trade scales will ever surpass or replace legal-for-trade static truck scales,” Grell says. “You’ve got to have a lot of space, and to make it legal for trade it has to be a level approach – the length of the truck on either side of the scale. So, you’re tying up a lot of real estate and land, and a lot of concrete and rebar.”

Steve Graham, segment marketing manager for vehicle scales with Mettler Toledo, reiterates Grell’s point, saying the adoption of WIM scales will likely be on a case-by-case basis.

“There are still going to be tens of thousands of static scales out in the marketplace,” Graham says. “So the adoption rate is going to depend on, [if a company needs] a new scale or how much throughput they need to increase to get trucks through. We’ll still sell a lot of static scales in the years to come. This is just one option that we’re going to provide.”

Jack Kopanski

About the Author:

Jack Kopanski is the Managing Editor of Pit & Quarry and Editor-in-Chief of Portable Plants. Kopanski can be reached at 216-706-3756 or

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