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Monday, 16 June 2014

Adaptation model of car driving

In my PhD thesis from 1996, I developed a model of driver behaviour that was named the adaptation model of car driving. In this article I will present the outline of the model. In the thesis, a number of experiments were presented that were designed to test important elements of the model. All experiments were performed in a research car driving simulator and most of the studies were published in the scientific literature.

The main element of the adaptation model of driver behaviour is that it predicts that any factor that affects operational performance will 
  • normally result in an adaptation of behaviour on the tactical level, 
  • such that constant safety margins are maintained. 
Operational performance concerns the lateral control performance (steering) and longitudinal control performance (braking and speed control in general).

The model represented in the following figure.

This model states that several factors affect operational performance. For example, temporary states, induced by alcohol or marijuana, affect psycho-motor abilities while psycho-motor abilities affect operational performance. Also, vehicle related factors, situational factors and driving experience may affect operational performance in accordance with the adaptive control models. The effects on operational performance are perceived via a feedback loop by the driver, although alcohol and young age may inhibit this. 

If driving is self-paced, the driver adjusts behaviour on the tactical level by either increasing speed or decreasing headway during car-following if operational performance is improved, or by decreasing speed or increasing headway if operational performance deteriorates. 

If there are no opportunities to adapt behaviour on the tactical level, i.e. when the driving task is forced-paced, the driver may elect in allocate more effort to increase operational performance. 

Adaptation of tactical behaviour or effort allocation does not only occur as a response to momentary changes, but also in the form of an anticipatory response. This response is the result of learned associations between various factors and effects on operational performance allowing an adaptation of tactical behaviour in the absence of an effect on operational performance. For example, if the driver has learned the effects of rain on road friction and on operational steering performance, he may already choose a lower speed before these effects are actually experienced during a particular period of rain.

When drivers are not able to adapt behaviour on the tactical level for whatever reason, for example, 

  • because they are intoxicated with alcohol or drugs or 
  • impaired by fatigue or drowsiness, or 
  • because they are inexperienced, or they overestimate their driving skills, 

the risk of traffic accidents greatly increases. So the model has a direct link with driver safety. It also explains why vehicle factors aimed to improve safety often don't result in safety improvements in practice.

The complete thesis can be downloaded here.

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