The Mustang has standard head airbag curtains for front and rear seats which act as a forgiving barrier between the driver and outboard passenger's upper bodies and the window and pillars. Combined with high-strength steel door beams and lower side airbags this system increases head protection in broadside collisions. The Z4 doesn't offer side airbag protection for the head.
The Mustang’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 Mustang 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. A system to reveal vehicles in the Z4’s blind spot costs extra.
To help make backing out of a parking space safer, the Mustang has standard Cross Traffic Alert and Cross Traffic Braking automatically engages the brakes to help avoid a collision. BMW charges extra for Cross Traffic Warning on the Z4 and the Z4’s Cross Traffic Warning does not include automatic braking.
Both the Mustang and the Z4 have standard driver and passenger frontal airbags, front side-impact airbags, driver and front passenger knee airbags, front seatbelt pretensioners, 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 and driver alert monitors.

