Why is it Dangerous to Drive After Rain?

At some point almost everyone who drives or is learning to drive hears about the dangers of driving immediately after it rains. There is a simple, straightforward answer to why this particular time is more dangerous than before a rain or as dangerous as driving during a rain.

Rainwater not only causes the surface to be more hazardous, it also tends to create a layer of water/oil/grease that makes the surface more slippery. Rubber tires on modern cars are designed to grip well in most conditions and some designs are intended to move water away from the tire, improving traction.

However, when the road surface is made even more treacherous because of elements other than water drivers need to be more cautious. All vehicles – cars, trucks, motorcycles – leave small amounts of oil, lubricating grease and tire residue on the road. These collect on the surface or soak into the asphalt or concrete, staying near the surface. Rain will help break these items loose and spread them over the road. The end result is a greasy layer that gets between the tire and the surface of the road.

When this is added to the puddles of water and the reduced visibility during and after a rain, driving conditions are hazardous. If the road isn’t properly constructed the conditions can be even worse. Modern highways are designed to allow water to run off. They are slightly crowned (higher in the middle than at the edges). This helps clear the road surface during and after rain.

The first few minutes after a rain begins may be the most dangerous because the oil and grease on the road has just started to spread over the surface. With this slippery surface and the reduced visibility drivers should exercise extreme caution. Rain can eventually wash much of the film off the road, leaving it wet but perhaps not as slippery. This doesn’t mean drivers should be less cautious!

Much of the information from law-enforcement agencies and motor clubs emphasizes the danger of driving during a rainstorm or just after it rains, especially if this rain follows an extended dry spell. If it rains for a day or two the road may become less hazardous, but it still isn’t as safe as a dry surface during times of moderate temperatures.

There are a few things a driver can do to stay safe when driving during or after a rain:

1.) Allow yourself more time. You can then drive more slowly and still get there in time.

2.) Leave more space between you and the car ahead. You will need to put on the brakes a second or two earlier, braking gently. Leave yourself time and space to do this.

3.) Don’t set your cruise control unless you are on a multi-lane freeway and there are no cars around you.

4.) Use headlights and if it is raining too hard to see, stop until the weather clears. Time is not as valuable as safety.