A seat belt system includes webbing having a solid material that is configured to effect a shape or dimensional change in response to an activation signal. In a preferred embodiment, the webbing includes a first part and a second part, each having a wide end and a narrow end. The webbing is mounted with respect to a vehicle seatback so that the webbing is positionable across an occupant between the occupant's neck and the occupant's pelvis, and is characterized by the absence of an over-the-shoulder portion.