Visalia is one of the latest targets of federal patent-infringement claims over vehicle-tracking technology on city bus systems.

ArrivalStar S.A., a company incorporated in Luxembourg, has filed about 180 lawsuits across the U.S. since 2006 against manufacturers, software companies, retailers, transportation companies and, more recently, local government transit agencies to enforce a range of patents it holds. That includes about 50 cases that have been filed just in the first six months of this year.

Attorneys for the Boston area's public transit system who fought an ArrivalStar patent suit in 2010 said the company's attorney was using "shakedown" tactics.

But many public systems have settled by paying a license fee.

The most recent suit was filed last week against Visalia and the Bay Area city of Vacaville in the U.S. District Court in Sacramento. ArrivalStar and a related company, British Virgin Islands-based Melvino Technologies, allege that both cities' transit buses use vehicle-tracking and passenger-notification technology that infringe on their patents.

The Indiana attorney representing the companies said ArrivalStar owns 34 patents that all relate to some form of tracking a vehicle, package or item online or sending updates to mobile devices.

The patents were originally granted to inventor Martin Kelly Jones, who attorney Anthony Dowell said is involved with both ArrivalStar and Melvino Technologies. Dowell said ArrivalStar has licensed the technology to more than 200 users, including "almost all of the private suppliers of packages that track vehicle fleets."

What Dowell and his small law firm do is hunt down companies using vehicle-tracking technology in their vehicle fleets and, if they aren't licensed or using a system provided by a licensee, seek to enforce the patents -- first with a letter asking a company to stop using the offending technology or to license it for a fee. If that doesn't work, a federal patent lawsuit follows.

The attorney said some transit systems either design their own system or get it from an unlicensed source.

"At this point, with Visalia we don't know where they got it," Dowell said. "We sent a letter in May and received no response. When we don't hear back, the only way to get their attention is to file a lawsuit."

On the Visalia Transit website, icons depict the real-time location of all of the city's transit buses. Users can select individual bus routes and click on a bus icon to see when each vehicle will arrive at its next two stops. The website indicates that it is powered by a system called OTvia2, a product of North Carolina-based Digital Recorders Inc. The company filed for bankruptcy in March.

Visalia deputy city manager Leslie Caviglia said that the city has not yet been served with the ArrivalStar suit and cannot comment on the case.

While Fresno and Clovis both have their route maps and schedules available online, neither transit system's website offers the type of real-time tracking that is at the heart of ArrivalStar's strategy.

ArrivalStar's lawsuit tactics are described by detractors, including the San Francisco-based Electronic Frontiers Foundation, as "patent trolling" in which the broadly worded patents are the basis for asserting that increasingly ubiquitous systems to track buses, trucks, trains, cars and even packages violate the patent holder's rights.

"We think it's a bad patent, and we're leading a campaign to bust it," said Rebecca Jeschke, EFF's media relations director. "When these cities are sued, they either have to settle or fight -- both of which are very expensive -- or stop providing a valuable public service."

Besides Visalia and Vacaville, ArrivalStar has in recent years sued transit systems in Monterey and Salinas, North Carolina, New Mexico, New York, Washington, Ohio, Oregon, Maryland, Montana, Virginia and Massachusetts.

Dowell said that all of his firm's ArrivalStar cases have been settled before a court decision. Many defendants, he said, opt to settle by agreeing to license the technology. "The average settlement really varies, but most municipalities are licensed for $40,000 to $50,000," Dowell said.

Not everyone settles quietly, however. In 2010, attorneys for the Massachusetts Bay Transportation Authority clashed with ArrivalStar, writing in court papers, "The primary, if not sole purpose of ArrivalStar is to exact tribute from any person that ArrivalStar asserts is using inventions claimed in patents they purport to own. ... Shakedowns such as this one should be outlawed."

Two months later, the two sides agreed to a dismissal of the case. Court records don't indicate whether the dismissal was the result of a financial settlement or a determination that there was no infringement.