Consumers who purchase hybrid or all-electric cars want to save money on fuel but without sacrificing safety. This is why the Insurance Institute for Highway Safety (IIHS) tested four 2017 model year cars for crashworthiness, two of those cars powered by all-electric motors and two plug-in hybrid models.
The all-electric cars, the Tesla Model S and BMW i3, didn't fare as well as the Chevrolet Volt and Toyota Prius Prime, two plug-in hybrids that earned the coveted 2017 Top Safety Pick+ award.
To qualify for Top Safety Pick, a car must earn "good" ratings in five crash tests: the small overlap front test, moderate overlap front test, side, roof strength and head restraint tests. In addition, they must have available front crash prevention systems that earn an "advanced" or "superior" rating.
To earn the right to be called a Top Safety Pick+ car, all the above conditions must be met and a car must also come with a "good" or "acceptable" headlight rating.
One of the tests conducted by IIHS is called the small overlap test, known for causing more problems to automakers than any other test. Tesla had altered the Model S because of the challenging test, primarily by making the side curtain airbags longer. But the car still had a few problems with the test when the seat belt allowed the torso of the test dummy to move forward to the point the dummy's head hit the steering wheel through the airbag.
A crash like that on a highway would typically cause injuries to the head and lower right leg.
IIHS made note that the Tesla Model S ratings apply to 2016-2017 models built after October 2016. Tesla had made changes in January 2017 to help with the small overlap test but more work apparently needs to be done.
The Institute also pointed out the difference in crash test results between the Model S and the smaller BMW i3, Chevy Volt and Toyota Prius.
The Volt, Prius and i3 technically did better than the Tesla Model S in the small overlap crash test, but IIHS says be careful about making much of a comparison. The Tesla Model S is larger than the other three cars, and since a crash depends on energy, the weight of a vehicle has an effect on the test results.
Researchers say the "acceptable" rating awarded to Tesla is in reality based on a more severe crash compared to the "good" ratings of the smaller lighter cars.
IIHS says the P100D version of the Model S didn't do as well on the roof strength test as other Model S versions, but the P100D is heavier because of a larger battery, so the P100D earned an "acceptable" rating.
Researchers also say the current Model S hasn't been rated for front crash prevention because the automaker hasn't activated the software for the automatic braking equipment, at least not with all the cars. In addition, the 2017 Model S so far isn't available with anything other than headlights that rate "poor."
The BMW i3 earned only an "acceptable" rating for head restraints and seats but earned "good" ratings in other tests. The i3 version with the optional front crash prevention system did well by reducing impact speed by an average of 9 mph in the 12 mph test and reduced the speed by 7 mph in the 25 mph test.
However, due to the lackluster head restraint and seat rating, the BMW i3 was the only 2017 model that didn't earn a "good" rating.
Testing on the 2017 Chevy Volt shows the difference between standard vehicles and cars equipped with optional safety features. The Volt can be purchased with an optional headlight feature called high-beam assist that automatically switches back and forth between high and low beams based on other vehicles being present.
Buying the Volt with this feature means a car that has earned a "good" rating for headlights, but without the high-beam assist, Volt headlights have an "acceptable" rating.
The Prius Prime is the plug-in version of the Prius hybrid, also a Top Safety Pick+ winner. Its standard front crash prevention system earns a superior rating and its only available headlights earn an acceptable rating.
Researchers also point to the mpg difference between the cars. Although the Chevy Bolt and Toyota Prius Prime can both run on gas, the Volt can allegedly travel 53 miles in electric mode while the Prius Prime can allegedly make it 25 miles without using gas.
However, when the cars haven't been plugged in, the Volt gets 42 mpg while the Prius Prime gets 54 mpg, at least according to estimates provided by the Environmental Protection Agency.
IIHS says it has plans to test another all-electric car as soon as it's available from General Motors. The automaker says the car is called the Chevrolet Bolt and should be available to the public later in 2017.