Insurers have a message for America’s truckers: Let us monitor your every move or we might take away your coverage.

Behind the push are surging losses for many insurance companies as an improved economy has led to more-crowded roads and more accidents. Meanwhile, smartphones have proliferated, increasing distracted driving. Last year, the commercial auto-insurance industry lost an estimated $716 million before taxes on policies, as costs totaled nearly $112 for every $100 of premium they collected, according to researchers at investment-management firm Conning Inc.

The business line’s underwriting results have been deteriorating since 2011, and are at their worst level since 2001, according to data collected from insurers by ratings firm A.M. Best.

To keep losses from repeating, insurers are increasing premiums across much of a business that generated $28 billion in premiums last year. Increases have ranged from low-single-digit percentages to 30% a year, companies and brokers say. Some insurers have even exited certain types of coverage altogether, including American International Group Inc.

Insurers are more likely to renew coverage, however, if a customer adopts sometimes-invasive technology. As a result, a wide range of commercial operators are installing cameras in the cabs of their vehicles, and cellphone applications to block use while a vehicle is in motion.

“We’re in the same boat as everyone else who operates a fleet in Atlanta: how to not lose our coverage,” said Ellis Lowe, human-resources manager at Estes Services, a heating and air-conditioning firm. “Insurance companies are tightening up.

Estes’s annual premium for auto insurance, in the low six figures, has risen more than 20% over the past two years, Mr. Lowe said. The firm just finished installing a program called Cellcontrol on phones of 112 technicians. The technology detects a vehicle’s motion and can be programmed to prevent drivers from any calling, app use, texting and emailing unless the vehicle is stopped, said Robert Guba, chief executive of Cellcontrol.

An insurance broker suggested the technology as a way for Estes to hold down future rate increases—and possibly avoid cancellation.

Many carriers have toughened their stance on writing new commercial-auto policies, said Lawson Burnat, a principal at the broker Pritchard & Jerden. “There is a lot more scrutiny. You have to be a lot cleaner risk” and focused on reducing claims, he said.

Insurance companies with the largest share of the commercial-auto market include Berkshire Hathaway Inc., Liberty Mutual Group, Nationwide Mutual Insurance Co., Progressive Corp., Travelers Co s., and Zurich Insurance Group AG’s Zurich North America unit, according to Fitch Ratings. Besides heavy trucks, the product line includes local contractors’ pickup trucks, buses, ambulances and cars used by sales forces.

Part of what is driving the losses: Many trucking firms hired inexperienced drivers to fill jobs after the recession, and they are more prone to accidents than seasoned ones. In addition, plaintiffs’ lawyers have increasingly targeted trucking firms as the deepest pockets in accidents.

There has been “an explosion of judgments and jury awards,” said Tony DeFelice, an executive at the insurance brokerage of Aon PLC. Some are known as “nuclear” verdicts, at tens or even hundreds of millions of dollars.

In the past, some employers were concerned about cameras and other monitoring devices because they had the feel of “Big Brother watching,” said Chad McGee, another Pritchard principal. But as premiums rise, companies are getting over the issue, he said.

Pittsburgh-based Beitler Trucking Inc. President Quentin Beitler said he was “looking for any technology that would help bring our claims down” when he saw a television program about onboard video cameras. He now has them in 45 trucks.

If there is a triggering event such as slammed brakes, these create video of the seconds just before and after the event. The video can exonerate a driver if wrongly accused of causing a crash, and it can help the firm coach its drivers if necessary, Mr. Beitler said. Across the industry, drivers can be fired for serious driving problems, though dismissal policies vary by company.

The firm’s insurer, Zurich’s North America unit, reduced Mr. Beitler’s insurance bill to encourage the use of smart technologies, a spokeswoman said.

Paul Farrell, a specialist in commercial-auto insurance at Nationwide, said he spends “a lot of time talking to the presidents and CEOs [of tech firms] about what they have in the pipeline,” to help steer policyholders to promising safety gear. The insurer reduces the premium for some policyholders who use such equipment.

Even some commercial automobile firms that target regular consumers are making changes.

AIG ran a pilot project last year with a European rental-car policyholder to test ways to reduce the number of wrecks of their rental cars. Under it, the rental-car firm encouraged its customers to participate in a program to assess driving skills, such as how smoothly they applied the brake when approaching a red light. The appeal to the customers was the chance to compete against each other for prizes for safe-driving techniques.

Following the project, AIG lowered the policyholder’s premium and the policyholder has continued the program beyond the pilot, AIG said.

“We think the key to making a difference is to provide real-time feedback to the drivers…and gamifying in some way that scores the drivers,” said AIG senior executive Lex Baugh.