For enhanced safety, the front and rear seat shoulder belts of the BMW 4 Series Convertible have pretensioners to tighten the seatbelts and eliminate dangerous slack in the event of a collision. The Porsche 911 doesn’t offer pretensioners for its rear seat belts.
The 4 Series Convertible’s pre-crash front seatbelts will tighten automatically in the event the vehicle detects an impending crash, improving protection against injury significantly. The 911 doesn’t offer pre-crash pretensioners.
The BMW 4 Series Convertible has standard driver and front passenger side knee airbags mounted low on the dashboard. These airbags helps prevent the driver and front passenger from sliding under their seatbelts or the main frontal airbags; this keeps them better positioned during a collision for maximum protection. Knee airbags also help keep the legs from striking the dashboard, preventing knee and leg injuries in the case of a serious frontal collision. The 911 doesn’t offer knee airbags.
The 4 Series Convertible has standard front and rear seat tall, head-protecting side-impact airbags, which act as a forgiving barrier between the passengers and the door. Combined with high-strength steel door beams this system increases protection from broadside collisions. The 911 doesn't offer rear-seat side-impact airbags, only ones for front seat occupants.
The 4 Series Convertible has a standard PostCrash iBrake, which automatically applies the brakes in the event of a crash to help prevent secondary collisions and prevent further injuries. The 911 doesn’t offer a post collision braking system: in the event of a collision that triggers the airbags, more collisions are possible without the protection of airbags that may have already deployed.
Over 200 people are killed each year when backed over by motor vehicles. The 4 Series Convertible 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 911 doesn’t offer automatic braking for stationary objects directly to the rear.
The 4 Series Convertible’s standard lane departure warning system alerts a temporarily inattentive driver when the vehicle begins to leave its lane and gently nudges the vehicle back towards its lane. A lane departure warning system costs extra on the 911.
The 4 Series Convertible has a standard blind spot warning system that uses sensors to alert the driver to objects in the vehicle’s blind spots where the side view mirrors don’t reveal them and moves the vehicle back into its lane. A system to reveal vehicles in the 911’s blind spot costs extra.
To help make backing out of a parking space safer, the 4 Series Convertible has standard Cross Traffic Warning, helping the driver avoid collisions. Porsche charges extra for Rear Cross Traffic Alert on the 911.
The 4 Series Convertible’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 911 doesn’t offer a driver alert monitor.
Both the 4 Series Convertible and the 911 have standard driver and passenger frontal airbags, front side-impact airbags, side-impact head airbags, four-wheel antilock brakes, traction control, electronic stability systems to prevent skidding, daytime running lights, rearview cameras, available all wheel drive and around view monitors.