Because of the larger manipulation distances and the frequently installed vibration-absorbing seats (with extra vibration damping), restraint systems in commercial vehicles must meet other requirements than those in passenger cars; it was found that integrated seat/belt systems (belt anchorage incorporated in the seat) are required.
Five different types of integrated seat/belt systems were evaluated in frontal crash experiments at an impact speed of 35 km/h, using dummies in a truck cab on the catapult unit. The results were compared with those obtained with conventional three-point belts and with unrestrained dummies.
The experimental results showed that when the dummy was unrestrained or protected only by a lap belt (even if integrated) the upper load limits used as protection criteria were far exceeded because of the heavy impact on the steering wheel; this did not apply to three-point belt systems. Very favourable forward displacement kinematics were achieved when using special seats of adequate structural strength with integrated three-point belt systems; in this case the load on the occupants' bodies lies within acceptable limits, and the occupants do not hit hard against interior parts of the cab.
Further, the experiment showed that a vibration-absorbing seat with integrated three-point belt and additional supports fitted to the seat and backrest is the optimum solution.