Vehicle Stopping Distance On Wet And Dry Roads Explained
Last updated on March 20th, 2023 at 12:52 pm
When it comes to driving, being able to judge when to apply the brakes and how long it will take to stop is incredibly important.
Most people know that driving in wet weather can be more hazardous than driving in dry weather, but they may not know why this is.
In truth, stopping times in wet weather can be much longer for a few different reasons.
Thinking Time vs. Braking Time
When you’re considering how quickly a car can stop, or the stopping time, you need to consider two different actions that happen within this timing.
These actions, which lead to how quickly a car will stop, are known as the thinking time and the braking time.
Thinking time is your reaction time, or how long it takes for your brain to realize that you need to stop and for your foot to actually hit the brake.
On average, an alert driver who isn’t distracted should have a thinking time of roughly 0.65 seconds.
However, most drivers are slightly distracted at all times, either because they’re looking for a destination, other passengers in the car are distracting them in small ways, or there’s something else on their minds.
This makes the average thinking time, in actuality, closer to 1.5 seconds. This thinking time goes up if the driver is distracted by something happening on or near the road.
Braking time is how long it takes for the car to come to a stop after you apply the brakes. Braking time depends on how fast you’re going, what the weight of the car is, and what the weather is like.
Cars driving on a dry road stop much more quickly than cars traveling down a wet road.
Why do cars stop faster on dry roads as opposed to wet roads?
When you apply the brakes on your car, the tires slowly reduce their spin, gripping the road and causing more friction.
Eventually, this friction causes the car to come to a stop. When the road is dry, car tires can grip the road well, and friction is increased, which in turn increases stopping times.
However, when the road is wet, moisture fills in any tiny gaps in the surface of the road, making it much smoother and more slippery. This reduces both traction and friction.
The more moisture, the more the friction and traction are reduced, causing the tires to slip and greatly reducing how quickly you can stop.
In general, stopping time is doubled on wet roads compared to dry roads. In order to stay safe and to ensure that you have enough time to stop, particularly when you’re on the road with other drivers or there’s an intersection coming up, it’s a good idea to reduce your speed by one-third of what it would normally be.
What is hydroplaning?
Hydroplaning happens when water comes between the car’s tires and the surface of the road faster than the vehicle can push it away.
Essentially, when your car is hydroplaning, it’s not actually touching the surface of the road but is sliding on a very thin layer of water.
When you’re hydroplaning, you can lose control of the direction the car is going, and the brakes may not work as well.
This can lead to sliding or skidding, which can be frightening. However, if your car is hydroplaning, it’s very important to remain calm.
Take your foot off the gas and, although you might want to press down on the brakes, try to just gently pump them instead. Steer in the direction need to go, but don’t jerk on the wheel.
How does water depth make stopping harder?
Driving on roads that are damp and driving through a puddle can make a big difference when it comes to stopping times. On damp roads where water hasn’t pooled, hydroplaning is much less likely.
In addition, if less water collects on the road, that means there’s more surface for your tires to grip, which increases friction and decreases your stopping time.
When you’re driving through a puddle, though, or any area where the water is deep, the loss of friction is greatly increased, and it’s much more likely that the water will form a layer between the road and the tire of your car, causing longer stopping times and an increased risk of loss of control.
The tires on your car also make a big difference when it comes to water depth and stopping time.
Most car tires have deep grooves in them. These grooves help to pull water up or away from between the tire and the road, breaking up the surface of the water.
This increases friction and reduces the risk of hydroplaning. In deep water, though, the grooves fill quickly and can’t work as they were intended. It’s always best to avoid puddles whenever possible.
It’s also a good idea to get new tires any time the treads have worn down.
Does speed change how quickly a car stops?
Moving at a greater speed down the road increases your stopping time. At a faster speed, drivers must pay attention to the speed and controlling a faster vehicle, as well as to everything else happening around them.
This means their thinking time is increased, which directly increases the stopping time.
Braking time is also increased when vehicles are moving at a faster speed. Traveling faster means that the car has more momentum, so it’s hard to stop and the brakes must work more to bring the car to a halt.
In general, doubling your speed means that you’re quadrupling your stopping time. Saying exactly how long it will take a car moving at a certain speed to stop is difficult, as stopping distance doesn’t depend solely on speed.
However, you can estimate the rate if you know how quickly you stop when you’re going a certain speed.
For example, if it takes you 5 feet to stop when you’re going 10 miles an hour, it will most likely take you about 20 feet to stop when you’re going 20 miles an hour.
This means that if you’re going 40 miles an hour, it will take you about 80 feet to stop, and if you’re going 80 miles an hour, it will take you about 320 feet to stop.
Stopping distance on wet roads can be doubled when compared to dry roads.
What other factors affect stopping distance?
Many different factors can change your stopping distance. A heavier car, for example, will take longer to stop because it has more momentum thanks to its weight.
How worn your tires and brakes are can also greatly slow your stopping time.
If you’re tired or distracted, this can slow your thinking time.
