Modelling driver steering and neuromuscular behaviour

Doctoral thesis, 2014

This thesis challenges the traditional view of treating steering behaviour as a tracking task, instead treating it as a reaching task. Here, reaching refers to a fundamental human behaviour with the the intriguing characteristic of having a linear relationship between maximum speed and distance, effectively making the movement time constant. Historically, by contrast, human steering behaviour has been modelled as tracking, since it was assumed that drivers follow the road by applying continuous error-minimising control. Early on, it was found that linear control could to some extent represent human steering behaviour, but with a consistent non-linear error referred to as the remnant. Using instead the framework of reaching, as in this thesis, one can better explain even the non-linear parts of steering behaviour. In the analysis of data collected within the work presented here, it was found that up to 70 % of all steering behaviour can be modelled as individual reaching movements or, in the case of driving, steering corrections. It was furthermore shown that, by allowing the superposition of two such corrections, nearly all steering behaviour can be modelled. In addition, apart from control aspects, the heuristics used by the driver have also been studied. By modelling driver behaviour in various traffic situations, it was found that the angle to an aim point was the best stimulus for a steering action. Based on reaching theory and the aim point heuristic, a new driver model was developed and tested in three different situations: A double lane change, a head-on collision scenario, and a lead vehicle braking scenario. In open-loop simulations, the model showed good results when compared with observed behaviour, for all three scenarios. Furthermore, special care was taken to avoid parameter redundancy. The model could, in fact, be defined by using only one tunable parameter, representing the stress level of the driver. From the simulations, it was found that larger values of the parameter were required in critical situations compared the values used in normal driving. The neuromuscular aspects of the driver were also studied. The new driver model mentioned above was refined to include such aspects, using the fact that a reaching movement can be explained by antagonistic muscle pairs. However, since driving also involves limb stabilisation, muscle co-contraction is also relevant. In a separate experiment, involving both adults and children, the reaction to a sudden and unexpected torque disturbance was studied. The observed behaviour could be attributed to both the stretch reflex and an automatic subconscious cognitive action. The thesis also discusses some applications where driver models of realistic steering behaviour can be useful, focusing on active safety systems and autonomous vehicles.