NHTSA found that side impact airbags consisting of curtains plus torso bags reduce fatalities in near-side impacts by 31%, combination bags (which have both head and torso protection inone bag) reduce fatalities by 25%, curtain only bags reduce fatalities by 16% and torso only bags reduce fatalities by nearly 8%.

Curtain and side air bags are designed to protect occupants in near-side impacts, those to the sides of vehicles adjacent to where the occupants are seated. Four major types of curtain and/or side air bags have been available in the United States since 1996. However, by model year 2011, 85 percent of new cars and LTVs (light trucks and vans) were equipped with curtains plus torso bags for drivers and right-front passengers. Curtains that deploy in rollover crashes began to appear in 2002; by 2011 about 45 percent of new cars and LTVs were equipped with such curtains. Logistic regression analyses of FARS data through calendar year 2011 show statistically significant fatality reductions for all four types of curtain and side air bags in nearside impacts for drivers and right-front passengers of cars and LTVs:
Fatality Reduction (%)          Confidence Bounds

Curtains plus torso bags                 31.3                                      25.0 to 37.1

Combination bag                             24.8                                      17.7 to 31.2

Curtain only                                     16.4                                        3.0 to 28.0

Torso bag only                                 7.8                                         0.4 to 14.7

Corresponding analyses of far-side impacts do not show corresponding, large benefits for curtain or side air bags. Curtains that deploy in rollover crashes show a statistically significant effect in first-event rollovers: The estimated fatality reduction is 41.3 percent (confidence bounds, 22.5 to 55.5%). Analyses should be repeated in about 3 or 4 years, when there will be considerably more data available.