7.1.1 Effects of psychiatric conditions on driving
Psychiatric conditions may be associated with disturbances of behaviour, cognitive abilities and perception and therefore have the potential to affect driving ability. They do, however, differ considerably in their aetiology, symptoms and severity, and may be occasional or persistent. The impact of mental illness also varies depending on a person’s social circumstances, occupation and coping strategies. Assessment of fitness to drive must therefore be individualised and should rely on evaluation of the specific pattern of illness and potential impairments as well as severity, rather than the diagnosis per se. The range of potential impairments for various conditions is described below.
People with schizophrenia may have impairments across many domains of cognitive function including:
- reduced ability to sustain concentration or attention
- reduced cognitive and perceptual processing speeds, including reaction time
- reduced ability to perform in complex conditions, such as when there are multiple distractions
- perceptual abnormalities, such as hallucinations that distract attention or are preoccupying
- delusional beliefs that interfere with driving; for example, persecutory beliefs may include being followed and result in erratic driving, or grandiose beliefs may result in extreme risk taking.
People with bipolar affective condition may demonstrate:
- depression and suicidal ideation
- mania or hypomania, with impaired judgement about driving skill and associated recklessness, and/or
- delusional beliefs that directly affect driving.
People with depression may demonstrate:
- disturbances in attention, information processing and judgement, including reduced ability to anticipate
- psychomotor retardation and reduced reaction times
- sleep disturbances and fatigue, and/or
- suicidal ideation that may manifest in reckless driving.
People with anxiety conditions (including post-traumatic stress disorder) may:
- be preoccupied or distractible, and/or
- experience panic attacks or obsessional behaviours that may impair driving.
People with personality conditions may be:
- aggressive or impulsive, and/or
- resentful of authority or reckless.
These impairments are difficult to determine because impairment differs at various phases of the illness and may vary markedly between individuals. The impairments described above are particularly important for commercial vehicle drivers.