The topic for this week’s episode is Vehicle Dynamics and Passing.
Passing the vehicle in front of you is one driving skill we often do but don’t give it much thought. Once you decide to pass a vehicle in an urban environment, realize, and remember that you and your car will be spending a good deal of time in the wrong lane. To give you an idea of how much time and distance, consider this scenario. If you are traveling at 50 mph or 80KPH and passing the average sedan or SUV going 40 mph or 64 KPH, you will need about 10 seconds and 736 feet or 225 Meters to complete the pass safely.
Essential points you can use to help in the decision-making process.
- Is the car you are about to pass aware of your presence?
Sometimes it appears apparent that it is, but don’t assume the car in front of you is aware of your presence and that the driver will react rationally. Don’t assume the vehicle you’re passing has Blind Spot Detection System.
- Are there side roads ahead that may hide a car about to turn into your path?
Even if you can’t see them, assume they’re there.
- How long is all this going to take?
Do you have enough time to pass and get back in your lane? Estimating whether or not the pass is safe requires quick thinking. You haven’t got much time.
- Check your mirrors before you pass; it’s just good sense to check your mirrors before you make any move with your car.
There are some critical issues
A. The speed of the vehicle you are about to pass.
B. The speed of your vehicle
The critical issue is the difference in speed between your vehicle and the vehicle you’re passing. For example, if you are traveling 60 mph or 96.6 KPH and the vehicle you are passing is 40 mph or 64 KPH, you will be in the opposite lane for 450 feet or 137 meters and 5.3 seconds. Keep your speed at 60 mph or 96.6 KPH and change the speed of the vehicle you’re passing to 30 mph or 48 KPH; you will be in the opposite lane for 300 feet or 91.5 Meters and 3.5 seconds. The bigger the speed differential between vehicles, the less distance and time you will be in the wrong lane. Even a speed differential of 10 mph or 16 KPH between the vehicle you are passing creates a significant difference in the amount of time you are in the opposite lane.
C. When do you pull out to pass?
Start to pass from a safe following distance. Do not speed up directly behind a vehicle and then turn out suddenly to pass. The closer you are to the vehicle in front of you, the more you will have to move the steering wheel to drive around it. Always keep in mind the fundamental laws of physics, “Combining high speeds with a lot of steering can be harmful to your health.”
But how far ahead is far enough? There are so many variables that it is hard to come up with absolute numbers. The distance to pull out depends on your speed, the speed of the vehicle you are passing, and the length of the vehicles involved.
Also, the closer you are to the vehicle in front of you, the harder it is to see around them. You cannot safely pass unless you can see far enough ahead to be sure that you can get back in the lane before meeting any traffic coming from the opposite direction.
Many Security Drivers use SUVs as the Principal Vehicle. We need to talk about SUVs and passing. Due to their high center of gravity, you need to leave much more room between you and the car you are about to pass. You must start your pass sooner than you would if you were in a sedan. If the driver pulls up too close to the vehicle in front, the driver will need to make a sharper turn to pull around the vehicle.
D. When do you pull in front of the vehicle once you have completed the pass?
As you go by another vehicle, be sure there is plenty of distance between your vehicle’s right side and the left side of the other car.
You have not finished passing until you get back onto your side of the road or in the lane where you belong, leaving the vehicle you have just passed at a safe following distance behind you.
For example, if the vehicle you are passing is traveling at 30 mph or 48 KPH, and you are traveling 60 mph, or 97 KPH, leave 60 feet or 18 Meters clear before returning to your side of the road (20 feet or 6 Meters for every ten mph of speed differential).
A good rule of thumb is that you can usually be sure it is safe to return to the right side of the road when you can see the vehicle you have passed in your rearview mirror.
When it comes to passing, there are some “never-dos.”
- Never pass on curves.
- Never pass at intersections.
- Never pass when crossing railroad tracks.
- Never pass at night when you can’t see far ahead of you.
We mentioned that – “If the driver pulls up too close to the vehicle in front of them, they will need to make a sharper turn to pull around the vehicle they are passing. In an SUV, you need to leave yourself much room if you will attempt a pass.”
This scenario presents the driver with the difference between having sufficient time and distance to drive around an object, in this case, a moving vehicle in front of them, or not having the time and distance to make a smooth transition around the object. These two events are the difference between emergency maneuvering versus cornering which leads to the next discussion.
Emergency Maneuver vs. Cornering
Training to avoid an emergency is difficult for both the student to learn and the instructor to teach. When a driver is confronted with an emergency, the amount of turning, steering, and braking needed to get out of trouble are not predetermined; in fact, that’s why it’s called an emergency. When the driver is confronted with an emergency – it’s “Holy Stuff,” and then the driver goes to work. From a vehicle dynamics perspective, an emergency maneuver is different from driving through a corner. When driving through a corner, the energy applied to the vehicle’s center of gravity is being applied relatively slowly and smoothly. I know it does not seem slow from inside the vehicle, but from the vehicle dynamics point – it is.
There is a big difference between energy applied to the vehicle going through a corner at speed and the energy applied to a vehicle during an emergency maneuver. In an emergency, a massive spike of energy is applied to the vehicle’s center of gravity.
Again, the driver does not purposely put a high spike of energy on the vehicle. Consider that if they are moving at the rate of 40 MPH or 64 KPH and an obstacle is in their path 75 feet 23 Meters away, they are 1.25 seconds away from the obstacle. Since it is a surprise, the driver’s reaction time will eat up at least half a second. At that point, the driver has to apply enough energy to move the vehicle away from the obstacle and not too much energy that would cause the vehicle to go out of control and do all that in a couple of tenths of a second, in the blink of an eye.
The event’s success will depend on the vehicle’s speed, how quick the steering wheel is moved, and the student/vehicle capability. Racing fans may consider the following blasphemy. But when the vehicle’s center of gravity gets hit with a large spike of energy, it does things that would challenge the best racer. The driver will need to perform an emergency maneuver with a vehicle that has about 75% less handling capability than the average race car. That is one hell of a dance. The skill needed to drive out of an emergency is not something you learn driving lines and apexes. It is a skill learned in the lane-change exercise. The exercise’s dimensions, the speed the students enter, and when the signal is given for the lane change all need to be synchronized. It is one of the most valuable skills taught when it’s all together and working.
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