2017 Tesla Model S initially had earned an acceptable rating in the small overlap test, which represents the type of crash that occurs when the front driver-side corner of a vehicle hits a tree or utility pole or collides with another vehicle. The main problem with the performance of the Model S was that the safety belt let the dummy’s torso move too far forward, allowing the dummy’s head to strike the steering wheel hard through the airbag.
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Tesla made changes to the safety belt in vehicles built after January with the intent of reducing the dummy’s forward movement. However, when IIHS tested the modified Model S, the same problem occurred, and the rating didn’t change.
Although the two tested vehicles had identical structure, the second test resulted in greater intrusion into the driver’s space because the left front wheel movement wasn’t consistent. Maximum intrusion increased from less than 2 inches to 11 inches in the lower part and to 5 inches at the instrument panel in the second test. The first test resulted in a good rating for structural integrity, while the second test resulted in an acceptable structural rating. The two tests’ structural ratings were combined, resulting in acceptable structure and an acceptable rating overall for the Model S.
The greater deformation in the second test also resulted in damage to the left front corner of the battery case. The deformation was limited to an area that didn’t contain battery cells in the tested vehicle, so this damage didn’t affect the rating. Higher-performance variants of the Model S could have battery cells in this area, but, according to Tesla, they also have different structure. They haven’t been tested separately and aren’t covered by this rating.
The Model S is only available with headlights that earn a poor rating and hasn't been rated yet for front crash prevention. While automatic braking comes standard, the software for the feature was only recently activated.