Combining modifications

The researchers found that the modifications work best when combined, and they may also require changes to the restraint system because of the modifications' effect on the movement of the crash dummies.

The most basic change the researchers identified was to strengthen the occupant compartment. At least one part of the door frame was reinforced on nearly every vehicle the researchers studied that rated a Top Safety Pick+. Among the vehicles whose structures held up best were those that have reinforced side frames tied into the main frame rail, providing an additional load path. Without the reinforced frames, crash forces generally go directly into the front wheel, suspension system and firewall. The result: major intrusion into the occupant compartment.

The IIHS researchers found that the steering column often moves to the right in the small overlap front crash test. When this happens, the front airbag moves as well, and the crash test dummy's head slides off the left side of the airbag. Some manufacturers addressed this issue by changes explicitly meant to limit steering column motion. For other vehicles, the reduced intrusion of the door frame and instrument panel was enough to increase steering column stability.

Restraint system performance wasn't always improved by better structural performance alone, however. In some cases, even though the steering column was stabilized and the restraint system redesigned, the crash test dummy contacted the front airbag on the left side and slid into a gap in the airbag protection.

On the horizon: safety improvements for back-seat occupants

In a related study, IIHS and the Children's Hospital of Philadelphia examined the characteristics of back-seat occupants injured in crashes to help manufacturers find ways to make rear seats safer. The front seat has gotten most of the attention, the IIHS researchers noted, while vehicle restraint system improvements for back-seat passengers haven't kept up.

Among all passenger vehicle occupants in crashes during 2007–2012, 12% were seated in back. Of that 12%, children younger than age 13 accounted for 56%, teenagers from 13 to 19 made up 19%, and adults were 21% of back-seat occupants.

Surprisingly, the study found that belted adults age 55 or older seated in the back had the highest risk of any age group of sustaining a serious or fatal injury in a crash, and they had a higher relative risk of death when seated in the back as compared with the front. The challenge for auto makers is to improve restraints for adults while not interfering with child restraints as most car seats for children are designed to be used in the back seat.

IIHS recommended as one option that manufacturers develop advanced restraint systems tailored for the back seat, such as inflatable safety belts. IIHS noted that Ford offers optional inflatable belts in certain rear seats of the Ford Explorer, F-150 SuperCrew, Fusion, Flex and Taurus, as well as the Lincoln MKT and MKZ. The Mercedes S-Class also offers inflatable belts, which are intended to reduce chest injuries by distributing crash forces more widely over the body than with conventional seat belts. The inflated belt also provides support for the head and neck to prevent excessive motion. The researchers also recommended front, side and knee airbags for the back seat, similar to those already in use in front passenger compartments.

NHTSA considering action

The National Highway Traffic Safety Administration (NHTSA) also is considering changes to the New Car Assessment Program to focus on rear-seat restraint system performance. According to IIHS, NHTSA is looking into creating a crashworthiness rating for rear-seat child occupant protection and running frontal tests using a crash test dummy representing a 108-pound, 5-foot tall woman or child seated in the back.

Despite all the statistics, the 2015 models are safer than ever. Still, you can lower your risk of injury in any car by wearing seatbelts, using appropriate child restraints and avoiding distracted driving.