Spurred to action when a wheel spun off one of its vehicles about two years ago, a Wisconsin company that operates some 900 school buses has fitted most of them with a simple device that shows at a glance when a lug nut is loosening.

Lamers Bus Lines Inc., which runs school buses in 19 cities, has installed devices known as Wheel-Checks on about 80% of its fleet, Dean Brown, general manager of the firm's Milwaukee terminal, said last week.

"Granted, it takes a little time," Brown said. "But for the investment, it's next to nothing compared to what could happen."

A wheel that came off a semitrailer truck Nov. 8 killed physician Krishna Chintamaneni when it struck his windshield as he drove on I-43 in Glendale. It was at least the eighth death in the country this year caused by a truck losing a wheel.

Law enforcement and federal transportation authorities are investigating the accident that killed Chintamaneni. The truck believed to be involved has been impounded in Michigan. A lawyer for the firm that operated the truck, and for the firm that owned it, has said the vehicle was inspected a few months ago and approved for use.

Meanwhile, tape from a 911 call more than eight hours before the accident indicates that a motorist noticed a badly wobbling wheel on the truck as it traveled Highway 41 near Appleton.

Wheels can fail for many reasons, and a photo of the truck wheel involved in Chintamaneni's death suggests the lug nuts weren't a factor.

But lug nuts - the heavy fasteners that hold a wheel to an axle hub - have been implicated in other wheel detachments.

One expert, John Woodrooffe of the University of Michigan Transportation Research Institute, believes a primary cause of those problems is nuts literally backing off their studs because they weren't tightened correctly.

Brown said no one was seriously injured when the Lamers bus lost a wheel.

"We just dodged a bullet with it, basically," he said.

Afterward, searching for ways to prevent such incidents, the company learned of Wheel-Checks.

The devices are made by a small Canadian company based on the design of an English inventor, said Stefni Walters, vice president of Toronto-based Wheel-Check Ltd.

Formed from bright plastic that stands out visually, they consist of a ring that fits tightly around the nut and another end that is pointed. A mechanic mounts the devices on the nuts so the points form a simple pattern. A driver checking his truck should be able to tell if a nut loosens because the pattern will be broken.

"When you walk up to that vehicle it takes little or no effort" to make sure the nuts are properly secured, Brown said.

Deaths by wheels spinning off make up a tiny sliver of the roughly 5,000 fatalities a year involving heavy trucks, and in any event, devices that show a nut is moving aren't foolproof. A 2006 study for the United Kingdom's Department for Transport found that some wheels equipped with movement indicators still had problems.

"This shows that adding these devices alone will not eliminate the problem, although it may well reduce it, and good maintenance will still be required," the study said.

Jim Tipka, vice president of engineering for the American Trucking Associations, said the wheel detachments he's familiar with stemmed from improperly adjusted bearings or problems with seals. Motion indicators on nuts, though, sound like a step in the right direction, he said.

"Anything that gives the operator a visual check is a good idea," Tipka said.

Like Lamers, trash hauler Waste Management Inc. uses Wheel-Checks on the several hundred trucks the firm operates in Wisconsin. Drivers must inspect their vehicles before and after their shifts, and the motion indicators tell them quickly if the lug nuts are tight, spokeswoman Lynn Morgan said.

Walters said Wheel-Check Ltd., which started about 10 years ago, expects to sell 3 million units this year. Last year, she said, the firm sold about 2 million.

"It's really starting to catch on," Walters said.