Here are a few sobering figures. When you’re driving, the grip of your car tyres ultimately determines how quickly it can stop. At 30mph, the tonne or more of moving metal you’re piloting is travelling at 45 feet per second; every second equals 2.8 car lengths. At 70mph, every second’s travel is 105 feet. In ideal conditions, a car travelling at 30 mph takes 75 feet to stop; at 70mph, it’s 105 feet. In wet conditions, the 30mph stopping distance jumps to 120 feet and at 70mph, it’s a whopping 560 feet – that’s 35 car lengths. The strategies for coping when driving in poor conditions aren’t all obvious but the need for them will become so. Read on and learn.
It’s clear that when driving in rain, we need to leave more stopping space, to give your car tyres room to work with their reduced grip. Reducing your speed is a good idea too.
Car tyres have more to deal with than just surface water. If it rains after a long dry spell, the road surfaces’ build up of dirt and diesel, plus water, makes for near skid-pan conditions. Moreover, it isn’t just car tyres that are affected by rain. It’s a fact that vision is compromised on many levels by rain. First, a rain-sodden windscreen isn’t the same as a dry one, regardless of how efficient windscreen wipers have become. Furthermore, any car has areas of unwiped glass. Second, clammier conditions lead to misting up. This can be cleared by demisters and heated windows, but this is rarely instant and it obviously affects vision. Third, heavy rain and the resultant spray compromises vision yet more. Fourth and last, pedestrians tend to shy away from the rain and are unlikely to keep as sharp a lookout as they might.
Apart from attending to the elements of speed, distance and grip, you need to take further care in wet weather. A flood, for example, can cause major problems. Drive into one too fast and your engine could inhale a measure of water. This could do anything from causing it to stop to doing irreparable damage. What’s more, even if you negotiate a flood successfully, you’ll have wet brakes. Apply your brakes lightly until you feel them start to work properly or they won’t be there when you need them. Also, remember that anti-lock brakes let you steer when skidding but won’t necessarily reduce stopping distance as much as you might think. In fact, a June 1999 National Highway Traffic Safety Administration (NHTSA) study found that ABS increased stopping distances on loose gravel by an average of 22 percent.
What about the still worse conditions of ice and snow, and fog. The former requires gentle, intelligent control inputs – you’ll soon find out how gentle you must be. Fog driving is all about vision. Some clearly feel they have magic tyres but the bottom line is if you can’t see or are following too close, you can’t stop in time, period. Remember to use your wipers when the fog droplets build up on your windscreen.
Lastly, it may seem odd to include ideal conditions, i.e. sunny, dry and bright, under defensive driving. If it does, try this. Picture yourself driving west, late in the day. The level sun is in your eyes, your windscreen’s grimy and your view of the road isn’t at all clear. This would be a good time to stop and clean your screen.