The 911 offers all-wheel drive to maximize traction under poor conditions, especially in ice and snow. The Z4 doesn’t offer all-wheel drive.
A passive infrared night vision system optional on the 911 helps the driver to more easily detect people, animals or other objects in front of the vehicle at night. Using an infrared camera to detect heat, the system then displays the image on a monitor in the dashboard. The Z4 doesn’t offer a night vision system.
The 911’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 Z4.
The 911 offers an optional Surround View to allow the driver to see objects all around the vehicle on a screen. The Z4 only offers a rear monitor and front and rear parking sensors that beep or flash a light. That doesn’t help with obstacles to the sides.
Both the 911 and Z4 offer rear cross-traffic warning, but the 911 with Rear Cross Traffic Alert also has Rear Cross Traffic Alert (automatically applies the brakes) to better prevent a collision when backing near traffic. The Z4’s Cross Traffic Warning doesn’t automatically brake.
Both the 911 and the Z4 have standard driver and passenger frontal airbags, front side-impact airbags, side-impact head airbags, front seatbelt pretensioners, four-wheel antilock brakes, traction control, electronic stability systems to prevent skidding, daytime running lights, rearview cameras, driver alert monitors, available crash mitigating brakes and blind spot warning systems.

