The 4 Series Gran Coupe has standard City Collision Mitigation, which use forward mounted sensors to warn the driver of a possible collision ahead. If the driver doesn’t react and the system determines a collision is imminent, it automatically applies the brakes at full-force in order to reduce the force of the crash or avoid it altogether. The S3 has a collision warning system without the crash-mitigating brake feature that could reduce stopping distances.
The 4 Series Gran Coupe 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 S3 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.
To help make backing out of a parking space safer, the 4 Series Gran Coupe has a standard cross-path warning system, which uses sensors in the rear bumper to alert the driver to vehicles approaching from the side, helping the driver avoid collisions. Cross-path warning costs extra on the S3.
The 4 Series Gran Coupe’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 S3 doesn’t offer a driver alert monitor.
The 4 Series Gran Coupe has standard BMW Assist, which uses a global positioning satellite (GPS) receiver and a cellular system to remotely unlock your doors if you lock your keys in, help track down your vehicle if it’s stolen or send emergency personnel to the scene if any airbags deploy. The S3 doesn’t offer a GPS response system, so if you’re involved in an accident and you’re incapacitated help may not come as quickly.
Both the 4 Series Gran Coupe and the S3 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, collision warning systems, daytime running lights, lane departure warning systems, rearview cameras and available all wheel drive.