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 S5’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. Audi charges extra for rear cross-path warning on the S5.
The Mustang’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 S5 doesn’t offer a driver alert monitor.
Both the Mustang and the S5 have standard driver and passenger frontal airbags, front side-impact airbags, driver and front passenger knee airbags, side-impact head airbags, front and rear 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, lane departure warning systems and rearview cameras.

