The Nissan Murano slams into a barrier as part of the IIHS small overlap crash test.

Only three of the seven midsize SUVs scored well in a series of front-end crash tests designed to simulate real-world accidents.

And only one of the 2015 models, the Nissan Murano, earned the coveted Top Safety Pick Plus rating from the Insurance Institute for Highway Safety, though the Ford Flex and Jeep Wrangler also passed the small overlap crash test designed to simulate what happens when a vehicle’s corner clips another car or a utility pole.

The test has posed some serious challenges for manufacturers and has led to a number of vehicle redesigns since it was first used in 2012. In the small overlap test, 25% of a vehicle’s front end strikes a barrier at 40 mph.

“The designation of the IIHS ‘Top Safety Pick Plus’ for the all-new 2015 Murano is exactly what Nissan expected for a vehicle that has always set the trends in its segment,” said Fred Diaz, a Nissan senior vice president, in a statement. “This Murano has once again raised the bar for midsize crossovers.”

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The Murano received a “good” rating in the small overlap test, the highest the IIHS offers. But it also is equipped with a forward collision mitigation system that can both detect a potential crash and, if necessary, apply the brakes automatically. That is one of the requirements for a Top Safety Pick Plus rating.

The boxy Ford Flex, which does not offer a crash mitigation system, had to settle for a Top Safety Pick endorsement. It was rated “acceptable” in the small overlap test.

The third vehicle to pass the test was the Jeep Wrangler, but the SUV did not get a Top Safety Pick rating because it scored only “marginal” in side and rear crash tests, the IIHS noted.

The passenger compartment of the Nissan Murano (l) compared with the Dodge Journey.

Another vehicle made by Fiat Chrysler was the worst performer in the small overlap test. According to the IIHS, the passenger compartment of the 2015 Dodge Journey partially collapsed, the side airbag failed to inflate, and the parking brake pedal tore through the crash dummy’s left lower leg. That earned the 2015 Journey a “poor” rating.

The maker tried to put the poor showing in a more positive light, declaring that, “No single test determines overall, real-world vehicle safety.” In a statement, the maker added that, “every FCA US vehicle meets or exceeds all applicable federal motor-vehicle safety standards.”

But IIHS Chief Research Officer David Zuby was less upbeat, in his own statement cautioning that “Chrysler, Dodge and Jeep have had some successes with redesigned models, but they haven’t done much in the way of interim improvements. As a result, they still have many models that rate poor or marginal.”

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While the Jeep Cherokee and Dodge Durango fared better than the Dodge Journey in the latest round of tests, they still got only a “marginal” rating. So did the Hyundai Santa Fe.

Including midsize models that were previously tested, the worst performer in the midsize SUV/CUV category was the Mazda CX-9. In previous testing of nine midsize models from the 2014 model-year, the Toyota Highlander earned a Top Safety Pick Plus rating. Four other models earned Top Safety Pick rankings: the Chevrolet Equinox and GMC Terrain, as well as the Kia Sorento and Nissan Pathfinder.

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