196 – Science of Winter Driving

For this week’s episode, we reach into the archives with the topic of the science of winter driving.

I know, I know, it’s not winter yet,  but the days and nights are getting cooler, and winter will be here before you know it. So we felt it was the perfect opportunity to discuss winter driving and secure transportation.

Listen to the Podcast

No doubt, driving in winter conditions can be challenging for all, including the Security Driver. Other drivers may have the option not to drive in winter weather, but not driving in icy and snowy conditions is not a luxury that most security drivers have.


An interesting metric from the ISDA Executive Vehicle & Secure Transportation Survey – Seventy percent of survey participants drive in winter conditions—this number aligns with the national (U.S.) average.

These are some facts and statistics that support the dangers of driving in a winter environment.

  • 17% of all vehicle crashes occur during winter conditions. (NHTSA, 2019) 
  • There are about 156,000 crashes annually due to icy roads. (Carsurance.net, 2020) 
  • Weather-related vehicle accidents kill more people annually than large-scale weather disasters. (The Weather Channel, 2018) 
  • It takes up to 10 times longer to stop on snow and ice than on dry pavement. (Geico Insurance, 2018) 
  • Freeway speeds are reduced by 3% to 13% in light snow and 5% to 40% in heavy snow. (FHWA, 2019) 
  • Each year, 24% of weather-related vehicle crashes occur on snowy, slushy, or icy pavement, and 15% happen during snowfall or sleet. (FHWA, 2019) 
  • More than 116,000 Americans are injured, and over 1,300 are killed on snowy, slushy, or icy pavement every winter. (Safe Winter Roads, 2019) 
  • Over 70% of the nation’s roads are located in snowy regions, which receive more than five inches (or 13 cm) average snowfall annually. (FHWA, 2019) (Source: https://driving-tests.org/driving-statistics/)

Type of Vehicle

Driving, any form of driving, including winter driving, is a balance. For decades we refer to that balance as the Security Driver Triangle. The triangle is made up of three components: THE DRIVER, THE MACHINE, and THE ENVIRONMENT.

When measuring driver capability, you cannot separate the vehicle from the driver; both contribute, along with the environment, to the driver and the principal’s safety and security.

A skilled security driver understands the effects that changes in the environment have on the vehicle driver combination. They work to anticipate vehicle behavior changes and are ready to maximize all of the vehicle’s capability. They know that driving in winter conditions significantly decreases the vehicle’s capability. The security driver understands various vehicles’ characteristics and their limitations – any vehicle, including All Wheel Drive (AWD).


There is a misconception of the capability of AWD and FWD in winter driving conditions. Most of the confusion comes from misinformation seen on T.V. Ads about AWD Vehicles. In one ad, the announcer talked about driving on “Black Ice,” 

He mentioned that if you press the correct buttons or switches on the vehicle, you solve the problems created by driving on black ice. PURE BS – Keep in mind that black ice is defined as a road covered with ice – unless the vehicle he is selling can alter the laws of physics –driving on black ice is dangerous and a challenge.

No matter what the T.V. ads show, no AWD or 4WD system will make up for a decrease in adhesion. When ice – snow – etc. creates less adhesion between the tire and the road, the vehicle’s capability to go – stop – and turn is greatly diminished.

A quick definition of AWD and FWD drive is in order. All-wheel drive refers to automatic four-wheel-drive systems where the vehicle selects two- or four-wheel drive based on road conditions. In slippery conditions, power is automatically directed to individual wheels with the best traction. This is especially helpful for getting out of snowed-in parking spots or tackling unplowed roads. However, drivers should keep in mind AWD does little to aid turning and braking on snow and ice.

The problem is that most 4WD/AWD drivers think they have a vehicle that can defy the laws of physics. No matter what vehicle the security driver is in, stopping on snow and ice will require up to 10 times the distance as stopping in normal conditions, and driving onto an off-ramp during black ice or wintry conditions will require a lot less speed than usual. The driver will have to anticipate that lower speed before they get to the off-ramp.

The Science of Winter Driving

If you are an ISDA certified driver or have attended an old Scotti School or Vehicle Dynamics Institute training program, you have been trained and measured to use 80% of the vehicle’s capability. That means that you can apply 80% of the vehicle’s weight pushing on the center of gravity of the vehicle either in a braking scenario – turning scenario, or a combination of braking and turning.

But when driving from dry conditions to ice (Black Ice), the traction to maneuver your vehicle decreases by 65%, so you suddenly have gone from an 80% driver to a 15% driver. This means you can only use 15% of the car to go stop and turn, not a pleasant thought.

Let’s use the science of driving and work the numbers to illustrate the danger of driving on ice or inclement weather. Consider that you were driving a 6000 lbs. Suburban that handles at .85 G’s., which means it can absorb 85% of the vehicle’s weight, pushing on the vehicle’s center of gravity.

Under normal conditions, meaning no snow or ice, when you move the steering wheel, the vehicle can absorb 5100 pounds (.85 times 6000) pushing on the center of gravity. As an 80% driver, you can apply 4000 pounds (.80 X 5100 lbs) to the Suburban center of gravity and life will be good – exciting but good.

A Scenario

Let’s create a scenario where you are driving a 6000-pound Suburban that handles at .85G’s, and you move from dry conditions to icy conditions. 

Again, using the science of driving, the following explains why you and your principal’s life is about to get exciting; who, we must keep in mind, pays you to drive him safely and securely.

You are now driving a vehicle that has gone from being able to absorb .85 G’s to accept only point .3GS or 30% of the weight of the vehicle; The .3 G’s represents a 65% loss in your car’s handling. So, now in a matter of tenths of seconds, you are driving a car that went from .85 G.S. know down to .3 g’s, quick arithmetic tells us you can apply 1800 pounds to the center of gravity; once you get past that number, refer to the get exciting mentioned above.

There is more bad news if you are an 80% driver – consider that you share that icy road with a substantial number of average drivers.

The average driver, as we have talked about for decades, can use only 40 to 50% of the vehicles capability, which translates to that they can apply only 720 to 900 pounds on the Suburban’s center of gravity before they slide off into the snow – hopefully not taking you with them.

Consider this if you have attended a Scotti School or VDI training program in the last 10 to 15 years. Imagine that you cannot drive through the slalom course at a speed greater than 25 without losing control; that is the difference between driving on ice on drive pavement.

Again, for those who have taken our training, we ask you to go back to the driver’s equation. If the coefficient of friction between the tire and the road surface is low, you only have two options; you can decrease your speed and limit your steering. But, since you may have to use the steering to drive onto an off-ramp, your only real option is to lower your speed.  


No 4WD or AWD system will make up for the 65% decrease in traction. If there is less adhesion between the tire and the road, the vehicle’s capability diminishes greatly. 

But using some simple math, consider that when you were driving on icy roads, the coefficient of friction is very low, so having the capability to use 80% doesn’t mean much because 80% of .1 is still a dangerous scenario.

That’s not to say that AWD is not useful in bad weather. It might be enough to get the vehicle up snow-covered hills and get the vehicle moving from a stop position where 2WD would not accomplish that.

Although this has been said many times and in many ways, stopping on snow and ice may require up to 10 times the distance as stopping in normal conditions. 

You can’t beat the laws of physics, so the only way you can survive driving in these conditions is to keep the speeds down. 

About the International Security Driver Association

The ISDA is a valuable resource for all practitioners working in the protection profession. We offer benchmark educational, networking, and marketing programs—access to the encyclopedia of executive protection and secure transportation – The ISDA knowledge center. The knowledge shared encompasses a wide range of topics with resources, information, and metrics for today’s practitioners.

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