STOCKHOLM – Autoliv Inc. has developed a new seatbelt concept that supplements the regular three-point seatbelt with a two-point belt so both shoulders of the vehicle occupant are strapped in. The seatbelt is currently being launched on Renault’s new electrical vehicle Twizy. 
Existing three-point seatbelt systems are very efficient in most crashes and for most occupants. They typically reduce the risk for serious head injuries in head-on frontal crashes by 45 percent to 75 percent but are less effective for other crash types, such as side impact or roll-over accidents.
By adding a two-point shoulder belt, the crash load on the occupant can be distributed over a wider area, according to Autoliv. This reduces the rib-strain by half, the company says, and is especially important for elderly passengers. The chest of a 60-year-old human can only withstand half as much load as the chest of a 20-year-old individual, according to Autoliv.
Additionally, with the added two-point seatbelt the occupant will be protected in all directions. This is important if the vehicle rotates, which is possible in oblique crashes and in crashes with a small overlap between the front-ends of the colliding vehicles, particularly in crashes involving a small car. Having dual seatbelts also reduces the risk of the occupant’s head hitting the inside of the roof in rollover accidents, Autoliv says.
Furthermore, the new seatbelt system offers enhanced safety in side-impact collisions, since not only one shoulder of the occupant but both shoulders are strapped in by a seatbelt. This prevents an occupant from being thrown or sliding out of the “open side” of a three-point seatbelt, when the vehicle is hit on the side where the occupant is not sitting. In those so-called far-side collisions, the occupant is hurled into the vehicle (due to the inertia force) and could hit hard objects, including the head of another passenger. In such far-side collisions, Autoliv says tests indicate that the company’s new supplementary vertical seatbelt over the occupant’s inner shoulder will reduce the risk for severe injuries and fatalities by approximately 30 percent.
While other four-point belt solutions exist, most of these seatbelts (such as four-point harness belts) require both hands for buckling up. Studies have shown that the inconvenience of such designs reduces seatbelt usage and, as a result, the potential benefits of the four-point belt system are lost.
