The belt airbags would be triggered in severe frontal collisions only (where they’re shown to be most effective), inflated by gas generators. The seat belt’s Velcro cover would split open during deployment, allowing the belt itself to expand to three times its normal width.
The belt’s larger surface area allows crash forces to be distributed across a wider area, lessening the chance of severe chest injuries. Research shows that the belt’s added thickness improves comfort under normal usage, too.
Don’t expect to see Mercedes-Benz deploy Beltbags for front seat passengers, as existing front airbag systems already protect first row occupants. Aside from adding to manufacturing costs, Beltbags would deliver no significant benefits to front passengers.
While Mercedes-Benz has a long history of pioneering safety advancements in automobiles, the Germany luxury brand wasn't the first to introduce rear seatbelt airbags. Ford debuted this technology as an available option on 2011 Explorer XLT and Limited models, and has since deployed rear seatbelt airbags on Ford Flex and Lincoln MKT models.