How to know when to stop driving, and how to have the conversation

Crash rates per licensed driver form a U-shaped curve, high among the youngest drivers, low through middle age, and rising again from around seventy-five. That much is well established and gets quoted constantly.

Two things are usually left out. The first is that per mile driven, older drivers' crash involvement rises, but a large share of the apparent risk is that they are far more likely to die or be seriously injured in a crash of a given severity — the fragility of the occupant, not the error rate of the driver. The second is that older drivers self-regulate more than any other group: they avoid night driving, motorways, rush hour, unfamiliar routes and bad weather, often long before anyone suggests it.

So chronological age is a blunt instrument. What matters is function.

The capacities that actually predict crash risk

Vision, and specifically more than acuity. Contrast sensitivity — the ability to distinguish an object from a similarly toned background — degrades with cataract and predicts crash risk better than the letter chart does. Visual field loss from glaucoma is significant and often unnoticed by the person, because the brain fills in. Cataract surgery has been associated with reduced crash risk in several studies.

Useful field of view, a measure combining processing speed, divided attention and selective attention. It is one of the better-validated predictors, and it declines independently of visual acuity.

Executive function — planning, judgement, inhibiting an inappropriate response. This is why frontal-type impairment is more dangerous on the road than memory impairment of similar severity.

Neck and trunk mobility. Prosaic, and it matters: if you cannot turn to check a blind spot, you are relying on mirrors alone.

Reaction time under dual-task conditions, which degrades earlier than simple reaction time.

Medication. Benzodiazepines, sedating antihistamines, opioids and some antidepressants are associated with increased crash risk. So is hypoglycaemia in a driver on insulin or a sulfonylurea.

Dementia and driving

A diagnosis of dementia is not automatically the end of driving. Mild dementia is compatible with safe driving in some individuals for a period, and several jurisdictions handle this through medical review and on-road assessment rather than automatic revocation. Moderate or severe dementia is not compatible with driving.

The complication is that insight is frequently impaired, so the person least able to judge their safety is the one making the decision. And progression means that an assessment showing safety today has a short shelf life — most guidance recommends re-review at six to twelve months.

Legal duties vary. In many countries the driver has an obligation to notify the licensing authority of a relevant medical condition, and in some the clinician has a duty or a discretion to notify. Anyone in this situation should establish what applies locally rather than assume.

The cost of stopping, which is real

This is the part that gets under-weighted in family discussions, and it is well documented. Driving cessation in older adults is associated with reduced out-of-home activity, shrinking social networks, increased depressive symptoms, accelerated decline in physical and cognitive function, and increased entry into residential care.

Some of that is confounded — people stop driving because they are declining. But longitudinal analyses that account for baseline health still find an effect, and the mechanism is not mysterious. In a car-dependent area, the licence is the infrastructure of an entire life: shopping, church, the golf club, seeing grandchildren, the ability to leave the house at all.

So "just take the keys" is not a neutral intervention. It trades one risk for another, and the second risk is borne entirely by the person losing the licence.

Having the conversation

Start early, before it is urgent. A conversation at seventy about what the signs would be, and what the plan would look like, is enormously easier than one at eighty-four after a near-miss.

Be specific rather than general. "You're getting too old to drive" invites an argument about age. "You've had three scrapes this year and you got lost going to your sister's" is a description of events.

Offer an assessment rather than a verdict. Occupational therapists specialising in driving assessment exist in most countries, and an independent on-road evaluation moves the decision away from the family. Many drivers accept a professional's judgement they would never accept from a son.

And solve the transport problem before removing the licence, not after. Set up the accounts, learn the bus route together, arrange the shopping delivery, work out who does the Thursday run. The reason people resist so hard is usually not the driving. It is the correct perception that nothing has been arranged to replace it.

If you are the driver

Get your eyes tested annually, including for contrast sensitivity and fields. Review your medications for anything sedating. Keep the neck mobile. Take a refresher course — several countries run them and insurers sometimes discount for it. Self-regulate deliberately rather than defensively.

And decide now, while it is abstract, who you would trust to tell you. Then tell them you have chosen them. It is a considerably better plan than waiting to be ambushed.