Abstract: A floor mounted auxiliary support rail of rail for a wide, bench type seat, provides extra load support intermediate the conventional, outboard seat adjuster tracks, as well as providing dynamic anchoring for the seat back and for a traveling seat belt support. A traveling seat belt support is slidably mounted to an auxiliary support rail by a pair of side by side rollers. Beneath the rollers, a pair of locking pins rest below a series of teeth in a rail slot. The rear locking pin is fixed to the seat belt support, while the front locking pin is fixed to an inboard seat back bracket support. The seat back bracket support is pivoted to the head of the forward roller, and the weight of the seat back continually holds the seat back bracket support, as well as the forward roller, down against the upper rail edge, and also holds both pins away from the teeth. A spring pulls the seat belt support back relative to the seat back bracket support, so that the rear roller is held down on the rail edge, as well.