Driving in a Wet Road

We often hear that driving in snow is treacherous and tricky. That the behavior of brakes is different on a wet, winter road from what one may see on a dry, clean, summer road. Well, last morning I had a chance to experience this during my driving class, in a controlled manner.

I started driving near Oerlikon, Zurich. Early in the morning of 28 Jan 2012 we had a bit of snow. Not really that much snow, so the streets within the city limits were already clean by the time I started driving. Most of the snow had either melted away or been cleaned by the city-service teams. When I started driving the streets were merely ‘a bit wet’. As we reached places outside of the city though, the road started showing signs of snow too, with a hint of suspicion about ice too:

When we reached an industrial area, where we had enough space to experiment with braking, I started accelerating from 0kmh up to 60 kmh and then trying to stop the car. The road was really wet at this point, and after a few repetitions two things were apparent:

• It takes a longer time to accelerate from 0 kmh to XX kmh on a wet surface.
  Traction is really important during acceleration time too. This is all,
  of course, obvious once you think a bit about what happens when the car
  accelerates. I tend not to think about it when driving on a dry surface though,
  so the surprise-factor when I observed what happens on a really wet road
  was pretty high.
• When braking hard on a dry road, there will often be a screetching sound
  and some level of tire wear-out, as tires ‘melt’ under the effects of traction.
  Quite the opposite happens when braking hard on a wet road: the tires lose contact
  with the road, resulting in very ‘bumpy’ braking behavior and much longer
  braking-distance.

At 60 kmh the braking distance on a wet surface more than doubled! The car also lost contact with the ground several times until it fully stopped, even if only for a fraction of a second. A speed of 60 kmh may seem relatively ‘high’, but it isn’t so uncommon. It’s merely 20% higher than 50 kmh, and there are many build-up areas near or around cities where 50 kmh is the average vehicle speed.

After the fact, thinking about our little ‘wet-road experiment’ seems scarier than it was when I was actually doing the driving. But it’s really nice that we did this. Now I have first-hand experience of what happens when the road is even moderately wet.

The wet-road experiment went really well. Looking forward to our next ‘car behavior’ driving/training hours.