By Samuel Smith
Last updated on: June 9, 2020 at 3:56 pm
Recent RAA road-safety calculations prove just how dangerous tailgating in wet weather can be.
Results from the study show an alarming difference between wet and dry stopping times, highlighting the importance of keeping your distance.
If you need to stop for an emergency at 110km/h on a dry road, it will take up to 104.2m. This includes an average reaction time of 1.5 seconds before you actually begin braking. Do the same in wet weather, and you will travel up to 149.6m before coming to a halt. That’s an extra 45.4m – nearly the length of an Olympic swimming pool.
“In wet weather, stopping times drastically increase no matter what speed you’re travelling,” says RAA Senior Manager Safety and Infrastructure, Charles Mountain.
“Naturally, high speeds pose greater risks, but even at slower speeds, there are potentially catastrophic consequences.”
According to RAA’s road safety calculations, if you’re travelling just 50km/h, it’ll take an extra 9.4m to stop in the wet. This may not seem like a lot, but it’s an increase of 29% compared to dry conditions.
At 80km/h, this increase blows out to a whopping 37%.
Relationship between speed and stopping distance*
*stopping distance = distance travelled while perceiving/reacting to the hazard + distance travelled while actually braking.
Calculations also showed a car driving on a wet road travels at alarmingly high speeds long after a car driving on a dry road has come to a complete stop.
Here’s an example: a car on a wet road and a car on a dry road hit the brakes at 50km/h. After the car on the dry road has come to a complete stop, the car on the wet road is still travelling 33km/h.
For vulnerable road users like pedestrians and cyclists, a collision at 33km/h could prove fatal.
Ramp the speed up to 80km/h, and the car on the wet road will be travelling 52km/h after the car on the dry road has stopped.
Mr Mountain says these extra braking distances, and speeds, should be a reminder for all motorists to adjust their driving to the weather conditions.
“Motorists should leave a greater space between themselves and the vehicle in front in these conditions,” he says.
“Drivers should be aware that pedestrians and cyclists can be harder to detect when it’s raining.”
Motorists should keep in mind that their make of car and tyre quality can impact stopping distances as well.
How much room should I leave?
RAA recommends drivers leave at least 3 seconds between themselves and the vehicle in front.
To figure out what 3 seconds looks like on the road, simply pick a fixed object and watch when the car in front of you passes that point. Then, count how many seconds it takes you to reach that same spot. No matter what speed you’re traveling, it should take at least 3 full seconds.
Stopping distance: dry vs wet
|Speed (km/h)||Dry stopping distance (m)||Wet stopping distance (m)||Increase (%)|