The S5 Sportback’s pre-crash front seatbelts will tighten automatically in the event the vehicle detects an impending crash, improving protection against injury significantly. The Legacy doesn’t offer pre-crash pretensioners.
Both the S5 Sportback and Legacy have child safety locks to prevent children from opening the rear doors. The S5 Sportback has power child safety locks, allowing the driver to activate and deactivate them from the driver's seat and to know when they're engaged. The Legacy’s child locks have to be individually engaged at each rear door with a manual switch. The driver can’t know the status of the locks without opening the doors and checking them.
The Audi S5 Sportback 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 Legacy doesn’t offer a front passenger side knee airbag.
The S5 Sportback has a standard Secondary Collision Brake Assist, which automatically applies the brakes in the event of a crash to help prevent secondary collisions and prevent further injuries. The Legacy 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.
When descending a steep, off-road slope, the S5 Sportback’s standard Hill Descent Control allows you to creep down safely. The Legacy doesn’t offer Hill Descent Control.
The S5 Sportback Premium Plus/Prestige has a standard Top and Corner View Cameras to allow the driver to see objects all around the vehicle on a screen. The Legacy only offers a rear monitor and rear parking sensors that beep or flash a light. That doesn’t help with obstacles to the front or sides.
Both the S5 Sportback and Legacy offer rear cross-traffic warning, but the S5 Sportback with Rear Cross-Traffic Assist also has Automatic Brake Activation (automatically applies the brakes) to better prevent a collision when backing near traffic. The Legacy’s Rear Cross Traffic Alert doesn’t automatically brake.
Compared to metal, the S5 Sportback’s plastic fuel tank can withstand harder, more intrusive impacts without leaking; this decreases the possibility of fire. The Subaru Legacy has a metal gas tank.
Both the S5 Sportback and the Legacy have standard driver and passenger frontal airbags, front side-impact airbags, driver knee airbags, side-impact head airbags, front and rear seatbelt pretensioners, height adjustable front shoulder belts, four-wheel antilock brakes, all wheel drive, traction control, electronic stability systems to prevent skidding, crash mitigating brakes, daytime running lights, lane departure warning systems, rearview cameras and available blind spot warning systems.