For enhanced safety, the front seat shoulder belts of the Audi A4 are height-adjustable to accommodate a wide variety of driver and passenger heights. A better fit can prevent injuries and the increased comfort also encourages passengers to buckle up. The Mercedes A-Class doesn’t offer height-adjustable seat belts.
Both the A4 and A-Class have child safety locks to prevent children from opening the rear doors. The A4 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 A-Class’ 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 A4 has a standard Audi Backguard System, which use a specially designed headrest to protect the driver and front passenger from whiplash. During a rear-end collision, the Audi Backguard System moves the headrests forward to prevent neck and spine injuries. At the same time the pretensioning seatbelts fire, removing slack from the belts. The A-Class doesn’t offer a whiplash protection system.
The A4 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 A-Class 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 provide maximum traction and stability on all roads, All-Wheel Drive is standard on the A4. But it costs extra on the A-Class.
When descending a steep, off-road slope, the A4’s standard Hill Descent Control allows you to creep down safely. The A-Class doesn’t offer Hill Descent Control.
The A4’s standard lane departure warning system alerts a temporarily inattentive driver when the vehicle begins to leave its lane. A lane departure warning system costs extra on the A-Class.
To help make backing out of a parking space safer, the A4’s optional rear cross-path warning system uses sensors in the rear bumper to alert the driver to vehicles approaching from the side, helping the driver avoid collisions. The A-Class doesn’t offer a cross-path warning system.
Both the A4 and the A-Class 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, daytime running lights, rearview cameras, available blind spot warning systems and around view monitors.
For its top level performance in IIHS driver and passenger-side small overlap frontal, moderate overlap frontal, side impact, roof strength and head restraint tests, its standard vehicle-to-vehicle front crash prevention system, its standard vehicle-to-pedestrian front crash prevention system, and its available headlight’s “Good” rating, the Insurance Institute for Highway Safety grants the A4 the rating of “Top Pick” for 2021, a rating granted to only 137 vehicles tested by the IIHS. The A-Class has not been tested, yet.