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Driving in fog and rain

Reduced visibility makes additional demands on drivers
Reduced visibility makes additional demands on drivers

Richard Russell,

October 15, 2012 — Concerned about driving in fog or rain? Here are some tips to help keep you safe.

How close is too close?
How close is too close?

Driving is a visual activity so it follows that when visibility deteriorates, so does the ability to drive safely. Each year we witness multiple-vehicle pile-ups, often with fog or rain given as the cause. 

Obviously, in those cases, the conditions had changed but the drivers had not. These same vehicles and drivers had co-existed when visibility was good – but collided when it was not. 

Stating the obvious, when the conditions changed, drivers need to make changes as well.

· Look far ahead

The most basic rule of driving safely is to look up, far enough down the road that you can read the traffic scene, giving yourself time to react. 

You can't avoid what you can't see.

Driving in conditions of reduced visibility is arguably one of the most dangerous situations you can encounter while at the wheel. 

Whether it be rain, fog, dust or snow, anything that reduces your ability to look well down the road should be seen as a warning signal to adjust your driving to compensate for that reduced visibility.

· Reduce speed and increase gap

In those conditions, the proper action is to reduce your speed and increase the gap to the vehicle in front. 

You can't react to what you can't see. So your speed needs to be such that you can safely stop the vehicle, if necessary, once you've seen a hazard.

If you are looking up, well down the road, you will identify reduced visibility conditions before you're into them, in time to ease off the accelerator and reduce speed and the gap gradually and safely. 

Hopefully the driver behind you is doing the same. If not you are likely to have company knocking at the back door. 

Driving into fog can happen unexpectedly
Driving into fog can happen unexpectedly

· The mathematics of following too closely

If you are driving at 100 km/h, you are covering more than 30 metres every second. 

The time it takes a young adult to react to a visual stimulus and get from the accelerator to the brake pedal, is about one-half second – if he or she is paying attention. 

The average is closer to a full second because most folks are thinking of something else, even if they're looking well ahead. 

Also consider that after age 20 our reaction times start to diminish.  

During the period between when the eyes identify an emerging situation and the muscles move the foot to the brake pedal you will have travelled at least 15 and more likely 30 metres – before the brakes are even applied! 

The average passenger vehicle is four-to-five metres in length so that's a minimum of four, and more likely six or seven, car lengths BEFORE THE BRAKES ARE EVEN ACTIVATED! 

At 120 km/h you’ll need five to eight lengths. 

It is not much of a stretch to see what happens when visibility deteriorates and speed does not, if the vehicle ahead slows or stops suddenly.
I once asked a friend, who is an accident reconstruction specialist, how they measure braking distances at a crash scene when the vehicle had ABS and the tires were not locked up and skidding, leaving a black trail. 

His answer? “Generally it is not an issue, because in most cases the brakes were not involved, the driver didn't have enough time or space to apply them.”

· Highway hypnosis

While maintaining a safe gap behind the vehicle ahead is important, it is not enough in itself to assure your safety.

Focusing only on the vehicle in front, just speeding up and slowing down to maintain that gap, can lead to what I call highway hypnosis. 

You lose sight of the bigger picture and everything else that's happening around you.

It's a particular temptation when your further visibility is limited by fog or rain. But, in effect, you're transferring responsibility for reading the traffic scene ahead to the driver you're following.

Is that really something you want to do? 

Look up, slow down, maintain a safe gap to the vehicle ahead, and drive within the limits of what you can see and safely react to.  That's your formula for driving in fog and rain.

This story was originally published on

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