Driving In Bad Weather

As mentioned in a previous article, driving is a system that consists of the Driver, the Vehicle and the Environment. We tend to focus on the Driver and the Vehicle, but both are at the mercy of the Environment. When the weather changes the environment the driving public can simply avoid the problem by not driving, but the police community or anyone who drives an emergency vehicle must cope with weather-related road conditions. Training your students to understand the affect the environment has on their capability to drive can mean the difference between being safe or becoming a statistic. Outlined below may not be a cure for the problem but it is information you can pass on to your students.

THE NUMBERS

Changes in the weather conditions can challenge the most experienced driver. As an example: you are driving around a normal run of the mill 90 degree street corner. If you drove the corner under dry conditions at max speed in a standard Crown Vic police vehicle the max speed would be approximately 41 MPH. (The definition of max speed is the speed you could drive through the entire radius of the corner without losing control) If the road was wet, max speed would be lowered to 36 MPH; snow would lower the max speed to 28 MPH and ice would lower it to 14 MPH. These are estimated speeds and may not be exact, but the purpose of the example is to show the dramatic change in speeds as conditions change.

Here is another way of looking at the example; driving from dry conditions to ice decreases the capability of the vehicle by 65%; driving from snow to ice decreases the vehicles capability by 49%. This decrease is the laws of physics at work, when moving from one surface to another; you are suddenly driving a car with much less capability. To make life more exciting this change in capability all happens in tenths of seconds. This quick change in vehicle capability would be difficult for the most experience driver to control.

TRAINING

If training includes a skid pad it would be a good idea to get the accident reconstruction guys to measure the coefficient of friction of the pad. You can relate the numbers to actual road conditions. If the surface coefficient of friction represents a wet condition that is good, but the students are not experiencing what it's like to drive on ice. The difference between rain and ice is a 60% decrease in vehicle capability.

This is a good place for the skid platform. As a side note, it is my opinion the Skid Platform is underutilized; one of its attributes is that it can create the conditions we are talking about - rapid changes from one environment to another. In a training program we conducted for a federal agency with skid platforms we set the platform so we could change the coefficient of friction of surface from dry conditions, to ice, to snow, to rain, all on a 1.5 mile course. This was a group of experienced drivers, with a lot of driver training. If the ice conditions occurred in a straight portion of the course, they could handle the problem, but if the ice occurred while turning it was difficult to control. If they had enough time and distance to slow down before starting the turning, they could drive through the corner. This all can be created and coached using the skid platform.

4WD/AWD

No 4WD system will make driving safer, especially in snow and ice. If there is less adhesion between the tire and the road, the vehicles capability is greatly diminished. The problem is that most 4WD/AWD drivers think they have a vehicle that can defy the laws of physics. However, once the vehicle is moving the laws of physics for all vehicles are equal.

Yes 4WD gets you 100% more traction than 2WD. That's good, but 100% of very little is still very little. The CF (coefficient of friction) for an icy road is about .1 to .15, so a 100% increase brings the CF up to .2 to .3 still creating an exciting ride.

I'm not saying that 4WD is useless in bad weather. It might be enough to get vehicle up snow covered hills and to get the vehicle moving from a stop position where 2WD would not be able to accomplish that. However, it is not enough to drive at normal speeds during low traction conditions and it should never be considered as solving the problem.

CHAINS

Since I have painted a bleak picture of driving on ice and snow, I should talk about a solution. This may not apply to most readers but it is worth mentioning. Only tire chains increase traction of rubber tires on snow and ice significantly.

4WD/AWD: Snow chains should be mounted on all 4 tires this will give the vehicle the best Go, Stop and Turn capability. This is the ideal scenario, but the driver still needs to be cautious.

Here are some of the general bits advice you can pass along to your students.

Although this has been said many times and many ways, stopping on snow and ice may require up to 10 times the distance as stopping in normal conditions. Another way of looking at this is: At 40 MPH (not accounting for reaction time) on dry a dry road a car can stop in the distance from the pictures mound to home plate. (About 60 feet) If the road is ice covered it will need the distance of two football fields to stop. That 100% increase that 4WD supplies means that instead of taking two football fields to stop the vehicle it will now stop in the length of one football field.

This is another one of those warnings that everyone seems to know but most everyone pays no attention to. Be careful on bridges, overpasses and infrequently traveled roads, which will freeze first.

When driving in bad weather the best advice is slow down.