The tests, conducted by the Insurance Institute for Highway Safety, rate "active safety systems," which warn drivers of impending impact and, in some models, automatically hit the brakes. The systems rely on radar, cameras and lasers that measure distance from other vehicles or fixed objects, and they're considered an early step toward self-driving vehicles.
"Active safety systems have great amounts of promise," said David Strickland, head of the National Highway Traffic Safety Administration. "We want to see more of these systems in the fleet."
But the tests demonstrate that most manufacturers still have work to do in perfecting the systems.
The insurance trade group, for instance, found only minimal braking at 12 and 25 miles per hour in tests of the Infiniti JX SUV. The Toyota Prius V wagon scored so poorly that it didn't qualify for an IIHS front crash prevention rating.
But Subaru's EyeSight collision avoidance system prevented the automaker's Legacy and Outback models from hitting a target vehicle in both the 12 mph and the 25 mph tests, the insurance research group said.
Cadillac's Automatic Collision Preparation helped the General Motors brand's ATS and SRX avoid hitting the target in the 12 mph test. In the 25 mph test, the systems reduced the ATS' speed by 15 mph and the SRX's speed by 19 mph. Both the Subarus and the Cadillacs received "superior" test ratings.
Other cars getting superior ratings included the Volvo S60 and XC60, when equipped with the full collision warning and autobrake system, and the Mercedes-Benz C-class equipped with the German automaker's full safety system.
"Front crash prevention systems can add $1,000 or more to the cost of a new car. Our new ratings let consumers know which systems offer the most promise for the extra expense," said David Zuby, IIHS chief research officer.
Front-to-rear crashes are the most frequent on the road, so the systems could make a huge dent in injury totals.
"This is really the future of both automotive safety and safety testing," said Karl Brauer, an analyst at auto information company Kelley Blue Book. "The IIHS ratings will encourage more automakers to provide this level of protection in the coming years."
These systems are already improving safety.
An earlier analysis by the Highway Loss Data Institute found that forward collision avoidance systems have reduced property damage claims on some Mercedes and Acura models 14 percent. They lowered bodily injury claims -- in which the driver of one car is accused of hurting someone in another -- 16 percent in the Mercedes and 15 percent in the Acura.
"We are very supportive of this technology, and we would like to see NHTSA set a standard for performance that says if you have it, this is the way it should work," said Clarence Ditlow, director of the Center for Auto Safety, an independent advocacy organization.
Eventually, Ditlow said, he would like to see the technology as standard equipment on all cars rather than a pricy option.
So far, the institute has tested 74 mid-size cars and sport utility vehicles, all from the 2013 and 2014 model years. In addition to the seven that received superior ratings, eight earned "advanced" ratings.
The systems on those vehicles reduced the speed at which crashes occurred but did not prevent collisions.
An additional 31 models earned "basic" ratings. They are equipped with a system that alerts the driver to the risk of a crash but don't automatically trigger the brakes. "We want consumers to know that forward collision warning alone can help them avoid crashes, and it's a feature that's available on more models than autobrake," Zuby said.
To judge automated braking systems, the insurance group put each model through a series of five test runs at speeds of 12 and 25 mph on the track at the Vehicle Research Center in Ruckersville, Va.
An engineer drove the vehicle toward a metal-framed foam-and-vinyl target designed to simulate the back of a car. Sensors in the test vehicle monitored its lane position, speed, time to collision, braking and other data.
The insurance group said it started the tests in part to encourage automakers to speed development of the technology. European safety regulators are using a similar protocol to rate vehicles starting next year.
"We are moving forward with the electronics on vehicles," Ditlow said. "With all the distracted driving going on out there, that's a good thing."