How Sleep Deprivation Affects Road Safety

Driver Fatigue and Microsleeps:
How Sleep Deprivation Affects Road Safety

Driver fatigue can trigger microsleeps even when your eyes are open. Learn the science behind these blackouts and how to stay safe.

Fatigue rarely announces itself when you are driving. There is no warning signal from your body telling you to pull over. Instead, tiredness builds quietly after long hours, poor sleep, dehydration, or an early start at work. Your reactions slow and judgement weakens. In Singapore, many drivers experience this.

A study in Singapore found that nearly one in three taxi drivers (32.9%) showed clinically significant daytime sleepiness and fatigue, a level known to erode attention and trigger microsleeps behind the wheel.

These lapses may explain why many fatal crashes are recorded as "failure to keep a proper lookout" or "loss of vehicle control”, where drivers simply do not register danger in time.

Dr Licia Tan, Consultant, Department of Occupational Medicine, Sengkang General Hospital (SKH), explains how fatigue and microsleeps impair driving, why these risks are often underestimated, and what drivers need to understand before getting behind the wheel.

Understanding Driver Fatigue

1.  “I would know if I was too tired to drive”

If you drive the same routes daily, it is easy to mistake muscle memory for alertness. You might believe you would spot your own fatigue instantly, but on familiar roads, tiredness manifests as mental inattention rather than a struggle to keep your eyes open.

This “autopilot" state is deceptive. While your hands and feet continue to manage the car, your brain’s ability to judge complex situations quietly erodes.

"Driving is a cognitively demanding task that relies on sustained attention, quick reflexes, and decision making," explains Dr Licia Tan. "When you are tired, these functions decline before you realise it."

2.  What tired driving actually looks like for you

Fatigue rarely ends with you falling fully asleep at the wheel. Often, it shows up as small lapses you brush off at the time. You tell yourself you are just distracted or that it was a one-off moment.

In the list of warning signs below, each feels manageable on its own. Together, they are warning signs that your attention is slipping.

3.  How those moments turn into microsleeps

If you keep driving while tired, those lapses can deepen. This is where microsleeps come in.

It is easier to understand the danger if you look at distance, rather than just time.

At higher speeds, a few seconds without awareness is enough for your car to miss a bend or stopped vehicle, or strike someone who never had a chance to react.

That is why many serious crashes are recorded as failures to keep a proper lookout or loss of vehicle control. You are not choosing to ignore the danger – you simply never registered it in time.

4.  Why this happens on familiar roads

If you are driving along the expressway every day, you know the drill. After enough trips, the road feels so routine – you know where traffic slows, and which lanes move faster – that your hands and feet just take over automatically. Here is where the trouble starts.

That confidence makes your brain slow down, even if you feel completely awake. On familiar roads, your attention fragments into little lapses and microsleeps that reduce your ability to react when something sudden happens.

Why Are You Missing the Signs?

We often think fatigue means struggling to keep our eyes open, but the real danger is "inattentional blindness”. While your eyes may be open, your tired brain stops processing what it sees.

Since you cannot spot your blind spots, your passenger becomes the best alarm system. They will catch you fidgeting or veering off-lane before you realise. If they notice something, fatigue is already messing with your driving – it is time to pull over.

“Passengers might notice the driver becoming fidgety, veering off his lane or driving erratically,” says Dr Licia Tan.

How Long Can You Drive Before Fatigue Sets In?

Many people assume fatigue becomes dangerous after very long drives. Alertness actually begins to drop much earlier.

Studies show that driver alertness declines significantly after 2 hours of continuous driving. Beyond that, it becomes harder for the brain to maintain the level of focus driving demands. A severely fatigued driver can be just as dangerous as a drunk one.

_{“Being awake for 18 hours is similar to having a blood alcohol level of 0.05%, and 24 hours equates to 0.10%, which exceeds Singapore’s legal limit for driving,” says Dr Tan.¹}

The Long-Term Health Impact of Driving

Driving is a sedentary activity. Hours spent sitting in the car mean you are in the same posture for long stretches with limited movement, with few or no breaks.

What this does to your physical health

• Prolonged sitting increases the risk of high blood pressure, diabetes, high cholesterol and obesity, all of which drain energy and affect recovery from fatigue
• Poor seating posture and awkward steering angles place stress on your spine and joints
• Common outcomes include lower back pain, neck stiffness and hip discomfort, especially during long cross-island drives
• For drivers of heavy vehicles, whole-body vibration adds another layer of strain, contributing to chronic spinal stress and musculoskeletal issues

What this does to your mental health

• Long hours navigating expressways and city traffic raise overall stress levels
• Pressure to meet schedules and manage time-sensitive trips increases mental load
• Rush-hour congestion adds frustration and fatigue
• Difficult interactions with passengers can affect mood, sleep quality and emotional recovery

How to Take Better Care of Your Health on the Road

Looking after your health is about making small, repeatable habits that reduce fatigue and strain over time.

Fatigue always seems to hit at the worst times, like when you are stuck in a jam. Realising your attention is fading helps to snap out of autopilot mode. Even if you are stuck in the seat, there are small steps to help yourself out.