The Effect of Driver Positioning on the Dynamic Response to a Potential Accident Event

A major challenge in the further improvement in secondary (passive) safety is to develop systems that offer improved levels of protection over a greater range of crash conditions, and for a greater range of the occupant population. The position of the driver is one of the important variables that a 'smart' restraint system would be required to adapt to. The study presented in this paper was conducted in the TRL driving simulator as part of the research programme for the PRISM project and was a novel experiment designed to assess the driver's positioning during the pre-crash phase of an accident. Forty subjects were selected from TRL's subject database for this exercise. The study group was balanced for gender and age. The responses of each subject were recorded during five emergency events throughout a 27.7 km rural route. The emergency event was created by a car emerging from a side road and stopping directly in front of the subject requiring them to brake quickly to avoid a collision. The main conclusions from this study were as follows: In over 80% of emergency events, drivers kept their hands in the position they were in at the start of the event, rather than replacing both hands on the steering wheel. This suggests that drivers often do not return to the standard driving position before impact. A 'smart' restraint system that is able to adjust to the position of the occupant has the potential to improve the injury outcomes in accident scenarios such as this. The realism of the simulator was good, with 97.5% of subjects rating it as realistic or very realistic, thus supporting the validity of the results for a straight line braking event of this type. Each one of the forty subjects experienced five emergency events and, although the experiment was fully balanced with false initial positions and false events, subjects generally reduced the vehicle speed after the first event. The response to all five events was considered representative of an emergency situation although there were fewer collisions on events after the first. Consideration of the driver posture and back contact area found that the reactions on all events were comparable. All subjects braked during all of the emergency events. Thus, it can be concluded that during an emergency event such as this, where the obstacle is visible and the driver has the opportunity to react, that the driver's right foot will be positioned on a depressed brake pedal. During the braking manoeuvre drivers tended to straighten the arms (increasing the angle at the elbow) and push the upper torso rearward into the seat. Measurements of the pressure on the seat back showed that the contact area between the occupant's back and the seat increased by 27% during the emergency event. This increased contact occurred in the upper back and shoulder region. Drivers exhibited little lateral movement, with the major motion in the fore-aft direction. There was an average rearward movement of the head of 28mm. The fore-aft response of each subject over the five initial positions was averaged and analysed against the seated height of the subject. This was then compared with the seated height of the 5th, 50th and 95th percentile Hybrid III dummies. This resulted in an average distance between the tip of the nose and steering wheel at the end of the pre-crash phase of: 5th percentile - 482mm; 50th percentile -561mm; and 95th percentile - 574mm. For the covering abstract see ITRD E141807.