How much did vehicles improve in the front NHTSA crash test when a driver airbag was added?

The driver front airbag has been one of the greatest innovations in frontal crash safety, saving thousands of lives every year. NHTSA's full-frontal crash test, conducted since 1979, is considered a good test of vehicle restraint system effectiveness, namely seat belt and airbag systems. We already know that the time period where frontal airbags were being introduced corresponded to a large improvement in test results. But just how much did the average vehicle improve when a driver airbag was added?

For this analysis, I looked at 44 models that were tested by NHTSA both with and without a driver airbag. Furthermore, I chose these models because their airbag did not come with a redesign, so the non-airbag models and airbag-equipped models would be structurally identical. 

On average, adding an airbag reduced driver severe injury risk from 30% to 18% - which means that 40% of people who would have been severely injured with just a seat belt would be spared severe injury with both the belt and a bag. Statistically, this is significant at a 90% level and clearly shows the lifesaving potential of even the earliest driver airbag systems. 

33 of the vehicles saw a lower injury risk, 1 tied, and 10 showed a higher injury risk with a driver airbag. However, 7 of these 10 vehicles worsened by less than 5%, and these were vehicles that had performed well without an airbag that continued to perform well with the bag. At the other end of the scale, 10 vehicles saw a drop of at least 20%. 

Going by NHTSA's 5-star rating system and considering 3-stars or more as "passing", 30 of the 44 non-airbag vehicles passed, meaning nearly a third failed. 41 of the 44 airbag-equipped vehicles passed, meaning failure was very rare. 2 of the 3 airbag-equipped vehicles that failed were "on the line". 

When driver airbags were added, truly dangerous vehicles nearly went extinct.

The analysis also showed that while airbags helped passenger car safety, they were even more beneficial for trucks, vans, and SUVs. Passenger cars saw a drop from 25% to 15% on average, but trucks/vans/SUVs improved from 37% to 22%. 

The news gets even better for airbags. On average, adding a driver airbag made the head injury criterion (HIC) fall from 974 to 636 - a 35% drop. Chest G's dropped from 49.7 to 49.4 - less than 1%. 

For passenger cars, the HIC dropped from 880 to 595 (32%), and chest G's dropped from 47.5 to 47.0 (1%). In trucks/vans/SUVs, the HIC dropped from 1,086 to 686 (37%), and chest G's stagnated at 52.4. 

Chest compression - which only loosely correlates with chest G's - was found to be a better measure of serious injury risk, and was adopted by NHTSA in 2011 in lieu of chest G's; IIHS has used compression for their chest injury measurement since 1995. Chest G's on their own are generally considered to cause a high risk of severe injury only at levels greater than those typically seen in most of these tests. HIC, on the other hand, is still considered the gold standard for head injury measurement by crash test agencies worldwide. This means that in reality, the risks of severe injury probably dropped by even more than the percentages show, since the improvements in injury measures were almost exclusively to the head. 

In addition, airbags spread the load over the entire body, reducing the risk of facial fractures and other localized injuries. Even in the safest vehicles without airbags, the dummy's head usually struck the steering wheel. Given equal measured injury risks, a real person would be better off with a driver airbag than without. 

For a detailed breakdown of the 44 vehicles analyzed, see the chart below.