In the past twenty years hundreds of infants and young children have died after being left in vehicles, usually by accident. When turning the vehicle off, drivers of the 3 Series Sedan are reminded to check the back seat if they opened the rear door before starting out. The S4 doesn’t offer a back seat reminder.
Over 200 people are killed each year when backed over by motor vehicles. The 3 Series Sedan offers an optional Active Park Distance Control that uses rear sensors to monitor for objects to the rear and automatically applies the brakes to prevent a collision. The S4 doesn’t offer backup collision prevention brakes.
The 3 Series Sedan’s driver alert monitor detects an inattentive driver then sounds a warning and suggests a break. According to the NHTSA, drivers who fall asleep cause about 100,000 crashes and 1500 deaths a year. The S4 doesn’t offer a driver alert monitor.
Both the 3 Series Sedan and the S4 have standard driver and passenger frontal airbags, front side-impact airbags, driver and front passenger knee airbags, side-impact head airbags, front seatbelt pretensioners, plastic fuel tanks, four-wheel antilock brakes, traction control, electronic stability systems to prevent skidding, crash mitigating brakes, post-collision automatic braking systems, daytime running lights, rearview cameras, available all wheel drive, lane departure warning systems, blind spot warning systems, around view monitors and rear cross-path warning.
For its top level performance in all IIHS frontal, side, rear impact and roof-crush tests, and its standard front crash prevention system, the Insurance Institute for Highway Safety grants the 3 Series Sedan the rating of “Top Safety Pick” for 2017, a rating granted to only 231 vehicles tested by the IIHS. The S4 has not been tested, yet.