The GLS’ pre-crash front seatbelts will tighten automatically in the event the vehicle detects an impending crash, improving protection against injury significantly. The Ascent doesn’t offer pre-crash pretensioners.
The GLS offers an optional Post Collision Brake, which automatically applies the brakes in the event of a crash to help prevent secondary collisions and prevent further injuries. The Ascent 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.
Earlier warning of stopped traffic, traffic signals, dangerous road conditions, weather, or accidents, can keep driver's safer and prevent crashes. The GLS has Car-to-X Communication, a system that seamlessly communicates important warnings to the driver about impending danger, if they're available. The Ascent doesn’t offer a system that can receive automated systems from other vehicles.
The GLS 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 and moves the vehicle back into its lane. Only the Ascent Premium/Onyx/Limited/Touring offers a blind spot warning system.
To help make backing out of a parking space safer, the GLS has standard Rear Cross-Traffic Alert and Active Brake Assist automatically engages the brakes to help avoid a collision. Only the Ascent Premium/Onyx/Limited/Touring offers Rear Cross Traffic Alert and the Ascent’s Rear Cross Traffic Alert does not include automatic braking.
Both the GLS and the Ascent 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, plastic fuel tanks, 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 and rearview cameras.
The Mercedes GLS weighs 899 to 1799 pounds more than the Subaru Ascent. The NHTSA advises that heavier vehicles are much safer in collisions than their significantly lighter counterparts.

