Driver Knowledge Tests

Driving with limited visibility

tunnel-bright-entranceDepending on the type of driving you do, and where you do it, you might frequently have to deal with limited visibility. As long as you are prepared for it you can mitigate the dangers, so we’ll go through the common scenarios you will encounter and what to do. In many cases you will want to slow down until visibility improves.

Motorbike riders should be aware that they will be even less visible to drivers of other vehicles if there are conditions of reduced visibility.

Torrential rain

If you live in an area prone to tropical thunderstorms or torrential rain (which basically is most of coastal Australia in one form or another), then you’ll occasionally experience rain showers that are so heavy the wiper blades cannot keep the windscreen clear enough even on their fastest setting. The only thing you can do in this situation is to slow down and pay particular attention to the brake lights of the vehicle in front.

High beam headlights

Occasionally a driver will forget to dip their high beam headlights. Give your headlights a quick flash, and if that doesn’t work do not put your high beam headlights on as that just means both of you are driving towards one another being blinded. Look at the left side of the road away from the glare, and slow down to be safe.


The ‘Walkie Talkie’ building in Eastcheap, London, UK, is an example of a building where the shape of it reflects concentrated light into an area of the street – enough to melt bits of cars, apparently.

If you’re living in metropolitan areas then you will come across this phenomenon, but you will also find it in agricultural areas where large glasshouses can reflect the sun.

You may also find that some trucks have chromed sections which reflect your lights back at you.

During the day you should have sunglasses ready and may also be able to position your sun visor to block some of the glare; at night, sunglasses make driving dangerous as they will restrict your vision too much. Reflections off the back of other vehicles are usually worst when you are closest to them, so avoid tailgating. Hanging back a little means that your dipped headlights will be illuminating the road and not the rear of the vehicle.

Fogged windows

Fogging on your windows is caused by warm humid air inside the car hitting the cold glass. Because you are constantly breathing in the car, the air will have water vapour, and as air cools it cannot hold as much water vapour as warm air. This causes water to condense on the cool glass, and the glass becomes opaque.

Battling the condensation

  • We have heaters in the car to evaporate the fogging off the windows and warm up the glass. These mostly rely on engine heat blown through the vents, and therefore can be ineffective until the engine is warm.
  • Keeping your windscreen clean on the inside will increase the time it takes for fogging to begin as water likes condensing around dust particles.
  • Commercial anti-fogging products can be applied to the window
  • Running your air conditioning will reduce the humidity in the car, and will speed up de-fogging
  • Your rear window will have a demister – usually a series of parallel linear resistive conductors in or on the glass – basically a wire through which power is applied, and it heats up. On newer cars these will be on a timer to help with fuel economy (generating electricity uses fuel). You may also have them in your wing mirrors, depending on the model of your car.
  • Keep a cloth handy. There are special cloths you can buy which are more effective than just a rag.

Make sure you know how to quickly operate your air conditioning, heater and rear demister as sometimes fogging can happen very quickly, even after you have been driving a while.

Motorbike riders can apply anti-fogging agents to visors, and also keep visors slightly open or open the vents to allow air to pass over the visor.

Sun strike/sun dazzle

Sun strike or sun dazzle happens every day at dawn and dusk. In summer, though, this is less troublesome as it’s earlier in the morning and later at night, therefore the problematic rush hour periods are avoided. In winter the sun sits lower on the horizon and sun strike can be a problem for longer, especially in areas which are drier and less cloudy.

To mitigate against sun strike keep your windscreen clean (it’s much worse on a dusty or dirty windscreen), make sure you have sunglasses in the car, and use your sun visor. You can also use your hand to block the sun, but be careful that you are not blocking your view of other vehicles.

Hang back from the vehicle in front as you might not see their brake lights as easily – give yourself a little more room to brake, and also a little extra buffer for any vehicles behind you that might be tailgating you.

Motorbike riders will be particularly affected by sun dazzle if their visor is scratched or dirty.


Fog can reduce visibility to a few metres. Fog is worse to drive in if you have your headlights on high beam, so keep them dipped. Turn your fog lights on as this will help drivers following you see where you are. Remember to turn them off afterwards, though, as they are very bright and can dazzle other drivers.

Avoid the temptation to lean forwards to try to see more – you won’t, and it puts you at risk if you have an accident as your head will be too close to the airbag going off.

In the UK the Driving Standards Agency makes the following recommendations:

  • use your lights as required
  • keep a safe distance behind the vehicle in front. Rear lights can give a false sense of security
  • be able to pull up well within the distance you can see clearly. This is particularly important on motorways and dual carriageways, as vehicles are travelling faster
  • use your windscreen wipers and demisters
  • beware of other drivers not using headlights
  • check your mirrors before you slow down. Then use your brakes so that your brake lights warn drivers behind you that you are slowing down
  • stop in the correct position at a junction with limited visibility and listen for traffic. When you are sure it is safe to emerge, do so positively and do not hesitate in a position that puts you directly in the path of approaching vehicles.


Bushfires and burn-offs can create thick smoke in places. Treat it the same as fog, but also be sure that you are not driving into the path of a bushfire. Be sure to close your car vents and windows, too.

Bonnet latch failure

This is incredibly rare, but does occasionally happen. Bonnets have a two-stage latch. If the first stage fails then the second stage catches it, which is why it’s rare that the bonnet would fly up. It’s most likely if you have previously damaged your bonnet latch in an accident and haven’t fixed it.

If your bonnet flies up it will most likely smash your windscreen. Wind pressure will keep it pinned against the windscreen and your visibility will be virtually zero. Sometimes you can see underneath the bonnet, but the best option is to judge where you are by looking out the side window, and brake fairly firmly (without risking causing an accident). Put your hazard warning lights on, too and try to manoeuvre off the road.


Summertime can bring hay fever issues to some people, and that can cause sneezing fits. When you sneeze you close your eyes for a fraction of a second. If you begin a sneezing fit, slow down and try to pull over so that you are safe. If you have medication, be sure to take it.


There are different types of spray.

  1. Constant spray during or just after heavy rain will reduce visibility most often if you are following a heavy vehicle or a vehicle towing a trailer. Turn on your lights, drop back from the vehicle in front (you should be four seconds back at least, to allow for greater stopping distances), and use your wipers on the fastest setting.
  2. Spray can also blind you if an approaching vehicle hits a puddle. If you are paying attention to the road, you will spot these and be able to get your wipers ready.
  3. Trucks and large vehicles travelling in the opposite direction can cause spray. Again, you can anticipate this.

If the road is dirty, dirty spray is worse than normal spray. Keep your washer fluid level topped up in case you need extra clean water to clear a smeary windscreen.

Motorcycle riders will need to be ready to clear the visor.

Rapid changes in available light level

Rapidly changing light levels occur most severely coming in and out of tunnels. As we get older our eyes don’t accommodate these changes so readily, either. Coming into a tunnel from bright light you won’t be able to see what’s in the tunnel. Coming out of a tunnel into bright light will be blinding, too.

Using your headlights will help on the way into a tunnel. Having sunglasses ready for the tunnel exit will help on the way out.

Be sure to drop back a little further from the vehicle in front if the change is severe.

Shadows can also be problematic. Coming from bright sunshine into a heavily shaded area will reduce your vision of the road surface and direction.

Driving with an eye injury or one eye covered

Covering one eye is called monocular vision and reduces depth perception, most notably for items close to you, which makes parking and driving in heavy traffic much more difficult. If you are recovering from an eye injury and have one eye covered temporarily, be extremely careful when driving. You will have a much larger blind spot and reduced peripheral vision on the side opposite your good eye.

Note that different states (and different countries) have different regulations regarding whether you are allowed to drive after losing the sight in one eye (whether permanent or temporary). In New South Wales and Victoria, for example, you must wait three months after losing the sight in one eye before you are allowed to drive again, so you will have had some time to get used to the change in your eyesight. Check with Roads & Maritime if you are not sure.

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

Tagged with: , , , , ,
Posted in Advice, Car, Heavy Vehicle, Motorbike