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Driving drowsy – a comprehensive look at driver fatigue

Fatigue behind the wheel is dangerous. What do you know about your own mental/physical state, and the kind of tired you feel? And how could you apply this in your own personal situation to best mitigate the risks of being tired while driving?
Person getting some sleep to prevent driver fatigue

It’s a horrible feeling. Dry eyes, slow blinks, foggy head… and what was that? Did you just fall asleep for a few seconds? You aren’t really sure you remember the last few minutes of driving… because everything is feeling heavy, the road is so boring, and all you can think about is some restful sleep.

We get asked a lot about driver fatigue. That could be because it’s widely understood that most adults aren’t quite getting enough sleep at night to feel rested, or because a mistake behind the wheel can have enormous consequences.

Dozing off in a meeting might be embarrassing, but it’s unlikely to be fatal. Doing so while driving is a huge risk to the driver, passengers, and anyone else nearby.

This article aims to provide the basics of fatigue identification and prevention, but we also delve a little bit deeper. Do you know about all the different reasons you might be tired? What might fatigue be a red flag for?

Have you ever thought about what comes first - does driving cause fatigue or does fatigue worsen driving? And incidentally, did you know that the materials your car interior is made of can make a huge difference to how alert you feel?

Understanding driver fatigue

We spend a third of our lives asleep, and that’s because we need it! While sleep is a hugely researched component of our lives, it’s still not completely understood. We do know that without it, we can’t function.

Sleep deprivation has been used as a cruel torture method, and we know that most health outcomes are improved by enough time spent asleep. Things like learning and concentration are positively affected, mood is better, and healing almost always benefits too.

Here’s an inescapable fact: Fatigue-related crashes are twice as likely to be fatal - drivers who are asleep can't brake. (And in a short 3 second sleep at 100km you can travel the length of a rugby field without knowing it).

Being awake for about 17 hours has a similar effect on performance as a blood alcohol content (BAC) of 0.05 (that just happens to be the legal threshold for driving in New Zealand and is very roughly 3 standard drinks in under an hour for the average 90kg male). If you’re someone who would never drink and then drive – this is probably a confronting thought!

According to NZTA, in 2019 in NZ, fatigue was a factor in 17 fatal crashes, 85 serious injury crashes and 491 minor injury crashes.

But while we have laws to govern our driving after drinking, there are no specific laws to regulate fatigue, nor tests to check for it. Even if we could introduce ‘tiredness checkpoints’ it would be incredibly difficult and time consuming to fairly measure.

What makes driving while fatigued so hazardous?

So let’s take a look at why fatigue can make driving so hazardous. It causes a driver a number of problems including:

  • slowing down reactions/decision making
  • causing you to miss key things like traffic light changes
  • decreasing your tolerance for other road users (frustration and annoyance tempt you to take risks you otherwise wouldn’t!)
  • making it hard to stay in your lane and maintain the right speed
  • decreasing your alertness to things going on around you.

In short – all the things that are vital to good safe driving!

Warning signs

So what can you look out for? Early warning signs are things like:

  • noticing your thoughts wandering or drifting
  • making a silly mistake like missing a gear, road sign or exit
  • realising you’ve slowed unintentionally
  • braking too late
  • anything that you know means you’re tired. Not everyone reacts the exact same way!

What about more immediate signs? These are things that mean you really should get off the road as soon as you can. Things like if you:

  • notice yourself yawning
  • are blinking more than usual/have sore or heavy eyes
  • seem to have slower reaction times
  • are having trouble keeping your head up and looking forwards
  • notice your eyes closing for a moment or losing focus
  • don’t remember driving the last few kilometres
  • notice your speed creeping up and down
  • feel a loss of motivation or impatience

What can you do?

Of course, in an ideal world, you’d be able to predict you were going to be too fatigued to drive and be able to prevent it. (We’ll talk later about the more real, non-ideal world we actually live in, but for now we’ve at least included some concrete suggestions to make these things possible.) Here are some great things to try to do, to help prevent fatigue behind the wheel:

  • Get a good night's sleep before heading off on a long trip. You might need to prioritise this so it happens – for example if you’re going on holiday, can you add a half day beforehand so you’re all organised and relaxed, and don’t have to stay up late packing?
  • Don't travel for more than eight to ten hours a day. Again, this is doable with a bit of planning, though easier on for-fun trips than for work.
  • Take regular breaks at least every two hours. Setting a timer can help – two hours can pass before you know it!
  • Share the driving wherever possible. Sometimes it’s not. But if you can, consider it.
  • Don't drink alcohol before your trip. Even a small amount can significantly contribute to driver fatigue. For planned trips, this should be possible for everyone. And for the driving you end up doing spontaneously or urgently, at least make sure you stop drinking as soon as you know you’re going, and that as much time and rest have passed since you did last have a drink.
  • Don't travel at times when you'd usually be sleeping. It’s tempting to get a jump on traffic. But if you have a choice, don’t drive when your body would normally be cosy and horizontal.
  • Take a 15-minute powernap if you feel yourself becoming drowsy. Think about what helps you snooze, like getting extra warm and listening to some music, and use this to have a good powernap roadside if you need.
  • Know the warning signs for fatigue. See our handy list above, but also know your own personal signs.
  • Understand the effects of any medication you’re taking. Even if it’s something that seems pretty common and/or harmless!
  • Snack lightly – avoid heavy meals and stay hydrated. Keeping good snacks in the glovebox as well as a water bottle will help here. Sugary things will only help short term!
  • Know your rights and work out a way to speak up if your manager is pushing you beyond what you know is safe. This one is key for all the people who drive for work who we know are being pushed past their limits, whether subtly or directly. It might not even be another person – are you self-employed and working to unrealistic targets?

Myths about fatigue

Before we move on, here are a couple of myths about tired driving that we hear all the time:

A coffee / energy drink will keep me awake

Not true. Sleep is the only way to relieve tiredness. Neither caffeine, fresh air nor loud music will stop you from being tired apart from very temporarily. And what’s worse – these short-term fixes can actually make things worse. Why? Because they give a driver false confidence, telling you that you’re okay to continue driving.

Fatigue is only an issue on long trips/straight roads/boring drives

Any driver can suffer tiredness, even on short trips. Over 50% of fatigue-related crashes actually happen within 25km of where the driver started their journey. And while boring and long straight roads don’t help, fatigue crashes can happen anywhere!

Of course, one size doesn’t fit all. Some individual factors that might be important to be aware of:

  • Lack of sleep or poor sleep. This one sounds obvious, but what we mean is that the quality as well as the quantity of sleep is important. For example, if you have a medical condition like insomnia or sleep apnoea that means you don’t sleep well, (despite being in bed for 8+ hours) your driving could be affected. Maybe your sleep is frequently interrupted (hello shift work or new-born baby!), or there are a number of nights in a row where you aren’t getting quite enough good rest, that can have an effect too.
  • The sheer amount of time spent driving. Long hours behind the wheel driving will lead to physical and mental fatigue. It might seem like you aren’t ‘doing much’ behind the wheel but it’s actually incredibly tiring. More on this in a moment.
  • When you drive. Do you often have to drive when your body wants to sleep? Thanks to something called our circadian rhythm we experience regular and natural dips in alertness associated with our body’s rhythm. So if you drive early in the morning when you’d usually be asleep, you’ll feel more tired even if you’ve had ‘enough’ sleep.
  • Where you drive. We’ve already mentioned monotony - driving along boring stretches of straight road may lead to a loss of concentration. Could you vary your route?
  • Individual characteristics. Things like our age, current life conditions/mood, physical condition and use of alcohol/drugs also influence how fast we become tired and how well we cope with fatigue. One person might be able to sustain concentration longer than another – or, if you’re feeling low or unwell, you might be more susceptible than you were last week when you were feeling better.
  • Work/financial situation. If you have working conditions that (subtly or overtly) push you to break the law or not listen to your body, it will be harder for you to make safe choices. Or if taking a rest means less income in some way, that will be a much more complicated choice.  

We mention the above individual factors and constraints because we know that for this information to be helpful, it needs to be realistic and personalised. It sounds great to simply say ‘get at least 8 hours of quality sleep before driving’ but it’s more helpful if you are able to be realistic about what you can do. If sharing the driving isn’t an option, what is? What are your personal constraints, and what can you do?

But driving is just sitting!

At this point we’d like to mention another common misconception we hear a lot.

Think back to when you were in school or university, or whenever you last sat one of those brutal 3-hour exams. Sure, you were sitting down the whole time, not expending too much in the way of physical effort - but when you stepped out of that room, you felt completely drained – right?

It’s the same as when you’re driving: you’re constantly aware of what’s around you, reacting to what you see and what you hear, all while keeping your car moving at the right speed and in the right direction. Sure, your body is just ‘sitting there’, but it’s collecting information and responding to everything around you all of the time you’re driving.

And new research is showing that the emissions from various part of the interior of your vehicle (especially if it’s new) can actually cause quite toxic air conditions. The best recommendation at the moment is to air the car before you hop in, and crack a window regularly.

So driving can cause fatigue, and fatigue can worsen driving. It’s a risky cycle! Further linked to this – some people use risky driving as a way to stay alert. For example, the more tired they feel, the faster they’ll go, hoping it will help keep them excited and focused.

Fatigue as a red flag

At this point we’d like to note that most other fatigue resources focus on tiredness as inevitable and something that just 'happens'. Something to avoid the effects of, rather than to find the cause of or understand better. We’d like to make the case that instead of ridding ourselves of or managing a negative condition we could try to improve our overall wellbeing - with a positive side effect of less fatigue.

We started this article by saying how horrible it feels to be exhausted behind the wheel. But that’s not to say that all tiredness is a negative feeling. Much like hunger before a delicious meal, feeling tired can be a positive feeling, telling you you’re ready for rest, and that you will likely rest well.

But, when it’s not feeling so positive, it’s probably there to tell you something. Tiredness when you are being required to perform (for example through driving) is telling you that you aren’t up to the task. And tiredness in general, might actually be a sign of something more.

So, we want to talk a little bit about the fact that fatigue might be a red flag for wellbeing, and that there are many reasons for it. Enter ‘fatigue’ into any online symptom checker and you’ll notice how many different results come up. Many conditions and concerns have fatigue as a defining symptom. If you are feeling tired a lot, have a think about how long it’s been since you’ve felt energised. Is the tiredness worse/better at different times? Anything you can think of that might be causing it?

Different types of tired

Mental/physical tiredness, sleepiness and boredom are all easily confused. Low energy due to depression is different from the tiredness after a big night out, which is different again from the exhaustion chronic fatigue sufferers experience. An unfocused mental state or lack of capacity to take on a single new thing can be quite distressing and be lumped into the same pot of ‘tired’.

We’d like to suggest here that instead of getting rid of a negative condition we could try to improve wellbeing with a positive side effect of less weariness. Is there something bothering you, health and wellbeing wise? Can you imagine that if this were addressed or improved, that you would also feel less lethargic? The answer is almost always yes.

Sometimes stepping towards the issue and opening ourselves up to the potential for improvement gives us more options. For example, if we strongly dislike feeling tired, push away all thoughts of fatigue and decide to just ‘keep going’, it might make our resentment towards the situation (and thus the tiredness itself) much worse. It could be something like addressing evening activities, weight, being honest about mental health… what is on the wellbeing to-do list for you? And does it start with figuring out which kind of tired you are?

Interestingly many people see fatigue simply as a negative consequence of work. But this may be true only for externally imposed goals (i.e., those you’re paid to achieve) whereas meaningful/self-initiated work is often not tiring at all but rather invigorating.

One theory (called the Motivational Control Theory) says that actually fatigue is a protective mechanism to help us decide if the effort we’re directing towards a goal is worth the reward. That is – if we’re too tired to continue, we’ll stop and do something else, suggesting that perhaps that goal isn’t the right one to pursue.

In summary

Fatigue behind the wheel is dangerous. This is something most people know. Fatigue is complicated. This is something that most people probably haven’t thought about. What do you know about your own mental/physical state, and the kind of tired you feel? And how could you apply this in your own personal situation to best mitigate the risks of being tired while driving?

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