Driving home after a night shift

The most likely way shift work will seriously hurt you is not the years of night work. It is the drive home.

Why it is dangerous

Sleep deprivation impairs driving in a way comparable to alcohol — after roughly 17 to 19 hours awake, performance is similar to being at or near the legal limit in many jurisdictions. Coming off a night shift, most people have been awake considerably longer than that.

Three things make it worse than the equivalent amount of alcohol:

The impairment is invisible from the inside. The ability to judge your own fatigue is one of the first things to go. Alcohol at least has a known dose; fatigue does not, and self-assessment consistently underestimates it.

Microsleeps give no warning. Two to thirty seconds of sleep, eyes open, with no subjective sense of having gone. At 60mph, four seconds is a hundred metres of unattended road.

The timing is worst. The drive home from nights lands in the circadian trough or just after, which is the physiological low point of alertness independent of how much sleep you have had.

The signs — and what they mean

If you notice any of these you are already impaired:

• No memory of the last few miles.
• Drifting, or the rumble strip.
• Repeated yawning, heavy eyelids, difficulty focusing.
• Missing a turn you take every day.
• Feeling suddenly alert after feeling drowsy — this is not recovery, it is arousal after a microsleep.

The last one is the one people misread most often.

What actually works

A twenty-minute nap before leaving. The single most effective intervention available, and it is available at most workplaces if you look for somewhere to do it. Caffeine immediately before it kicks in as you wake, which is the standard combination.

Not driving after the last shift of a block. The cumulative version is the dangerous one. A lift, public transport or a taxi after the final night is cheap relative to the alternative.

Sunglasses. Not for alertness — for the sleep afterwards. But they also reduce the glare-fatigue of a low morning sun on the drive itself.

Cold air and loud music: no. These produce a brief arousal and no improvement in actual performance. They are what people do instead of stopping, and they are why “I opened the window” appears in accident reports.

Pull over and sleep if it starts. Twenty minutes in a lay-by is inconvenient. The alternative is not.

The bit worth planning in advance

The decision about whether you are safe to drive is made by the person least able to make it — you, at 07:30, after four nights.

Which means it should be decided before the block, while rested:

• “After the fourth night I don’t drive; I get a lift or I nap first.”
• “If I’ve been mandated over, I nap before leaving. No exceptions.”
• “If I catch myself drifting, I stop. I don’t finish the journey.”

A rule decided in advance is a rule you follow. A judgement made at the time is a judgement made by somebody impaired.

Employer responsibilities

Worth knowing: employers have duties around fatigue risk in most jurisdictions, and in safety-critical sectors these are explicit. Many workplaces have somewhere to nap, a taxi policy after mandated overtime, or a fatigue policy nobody has told you about.

Asking is worth it, and asking as a group is worth more. A rest facility gets provided far more often when several people request it than when one does.

For the household

If somebody in your house drives home from nights, two things help:

Do not schedule anything for immediately after they get home. The pressure to get somewhere is what stops people napping first.

Take “I’ll get a lift” seriously rather than as a fuss. The cost of collecting somebody at seven in the morning is an hour. The alternative has a different order of magnitude, and this is the single clearest place where visibility of the schedule pays for itself — knowing tonight is the fourth night is what turns a vague worry into a lift arranged in advance.