Episode 178 – The Science of the Lane Change

The topic for this week’s episode is the science of the lane change.

If you have been to an Advanced Driving, EVOC or Protective Driver Training Program, you have driven through a Lane Change exercise. It is a staple of most all driving programs.

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Over the years, feedback from former students indicates that the “Lane Change” exercise is one of the most important, if not the most important exercise, in a protective driving program. The comment we heard often is that the Lane Change instills life-saving skills.

The old Scotti School and now VDI call it the Lane Change exercise, but it has different names depending on the training provider. Names like – Evasive Maneuver, Accident Avoidance, or Swerve to Avoid. No matter the exercise’s name, they all have the same basic characteristics that are essential to all Protective Driving training programs.

The purpose of the Lane Change is to simulate an unexpected event that can occur anytime, anyplace, and with a minimum amount of time to react. As the student approaches the exercise, they know they will need to make a decision. The Lane Change exercise is not unexpected; the driver knows that a decision needs to be made, so the exercise is not a complete surprise.

One of the Lane Change exercise goals is to have the student experience high spikes of energy, pushing on the vehicle’s center of gravity, that come in a short time and distance. As we will discuss, it is that science of the time – distance and energy coupled with training and measuring the student’s ability to control that scenario that makes the Lane Change a life-saving exercise.

There are driving exercises like the slalom course that supply the student with the opportunity to control the energy applied to the vehicle’s Center of Gravity. But, there is a substantial difference in the skill set needed to drive around a corner at speed or through a slalom course compared to the skill required to control a large spike of energy hitting the vehicle and having little time and distance to control the vehicle and drive through the Lane Change.

The Lane Change also serves as a demonstration of the importance of time and distance and decision making. From an instructional point, the time and distance aspects of the Lane Change exercise are one of the most valuable lessons learned in any driver training program. Small changes in the design and execution of the exercise will create major changes in the outcome of the exercise.

The purpose of this podcast is to look at that aspect of the Lane Change. There are many variations of Lane Change design for this podcast; we will stay with the basic design.

The Maneuver

The basic lane change design consists of an entry gate, barrier, lane gates on each side of the barrier, and exit gate.  As the driver approaches the entry gate, a command signal is given by the instructor; that signal will require the driver to drive into one of the barrier lane gates, left or right.  This is one of the critical moments of the lane change exercise. If the signal is not given at the correct moment, it makes a massive difference in the outcome.

As an example, a student drives into the entry gate at a speed of 40 MPH. 64.4 KPH. If the command is given 12 Feet – 3.7 Meters in front of the entry gate, that is the same as providing the student .2 seconds extra time to react (40 MPH/64.4 KPH equals 58.8 feet or 19.9 Meters a second or 5.9 feet or 1.8 Meters every .1 second).

If the entry gate is 60 Feet or 18.3 Meters from the barrier gate and the signal is given 2/10 of a second early, the student now has 72 Feet or 22 Meters to execute the command. The 72 Feet or 22 Meters was derived by adding the additional 12 Feet or 3.7 Meters given to the driver because the signal was called 2/10 of a second earlier to the 60 Feet or 18.3 Meters from the entrance to the barrier.

Conversely, if the instructor gave the signal 12 Feet or 3.7 Meters past the entry gate, that would be similar to taking away .2 seconds of reaction time. There is a substantial difference between giving the signal 12 feet or 3.7 Meters before the entry gate or 12 feet or 3.7 Meters after the entry gate.

If the signal was given 2/10 of a second two late, the driver now has 48 feet to execute the command; the 48 Feet or 14.6 Meters is derived by subtracting 12 Feet or 3.7 Meters from the 60 Feet or 18.3 Meters.

So, by giving the signal 2/10 of a second early, an instructor can create an easy scenario. Giving the signal 2/10 of a second too late, the instructor has created a virtually impossible scenario for the driver.  By the way, 2/10 of a second is the time it takes a person to blink their eyes, so in the blink of an eye, an instructor can unwittingly change the exercise from do able to near impossible.

Miscellaneous Notes

Lane change exercises require that the speed be measured at a minimum of three locations: the entrance gate, the speed at the barrier gate, and speed at the exit gate. Measuring only the entrance speed simply makes no sense. We often hear students say they drove into the Lane change exercise at high speed, but It’s not as much as how fast they drove into the exercise; it is their average speed through the exercise again measured at the entrance, the middle and exit.

The critical moment for the driver is that time just in front of the barrier gate and just after the barrier gate; if the exercise is designed correctly, that is the location in the exercise where the highest energy is applied to the vehicle, which in turn means that that’s where the driver’s level of skill will be taxed, and the point in the exercise where the student ability to use the vehicle capability needs to be measured.

Another issue is how speed is measured. The speed cannot be accurately measured by an instructor sitting in the passenger seat. Frankly, that is comical. If, as a student, or a company sending your personnel to training, you’re spending a significant amount of dollars to go to a protective driving program, I can’t fathom why that training program cannot afford a radar gun to measure speed. At one time 40 plus years ago, radar guns were relatively expensive, but now the cost is minimal.

There is no logical reason why not to use a radar gun to measure the speed.  The advent of inexpensive onboard computers makes the task of measuring speed and the energy exerted on the vehicle accurate and simple. Measuring speed and the energy the driver applied to the vehicle is how driving competence is measured. Also, a computer supplies the instructor with the information needed to coach and measure the student’s ability to avoid an emergency maneuver. 

In our opinion, the Lane Change is one of the most dimensional and speed-sensitive exercises in driver training. Many training programs use lights to indicate what lanes the student should drive through, but that is susceptible to error. Verbally calling the signal is irresponsible.

The more sophisticated and professional driver training programs use a Doppler Radar  

Device. This device can measure the speed of the vehicle as it approaches the lane change entry gate. For example, VDI created an algorithm customized to work with the lane change and braking exercise that allows an instructor to program when the decision signal is activated according to the vehicle’s speed. 

The Doppler Radar algorithm can measure the vehicle’s speed as it approaches the lane change entrance gate; the algorithm turns on one of the signal lights at a preset time measured in tenths of a second and corresponds to a specific distance the vehicle will be from the obstacle. If the instructor wants the student to have one second to drive into whatever lane they pre-select, they will set the computer algorithm to accomplish that goal. They can vary the time in increments of a tenth of a second – which in turn changes the amount of distance they have to maneuver the vehicle, which creates the amount of energy the driver will need to control.

This type of measuring device allows the instructor to accurately demonstrate the importance of time and distance and the importance of quick decision-making. The algorithm, unique to VDI’s Doppler radar system, also randomly selects which options the driver is presented with.

Cannot stress the importance of timing – For example, if a Lane change is designed to accept an entrance speed of 45 mph, 72 KPH, calling the signal 2/10 of a second late will create a dangerous scenario for the driver.

At 45 MPH or 72 KPH, if  a signal that is called .2 seconds late would increase the energy on the vehicle by as much as 40%, changing the energy from the driver having to handle .66 GS to, in a blink of an eye, having to handle the vehicle at 1.1 GS a dangerous scenario.

The takeaway is that all driving exercises need to be designed with the utmost precision. A difference of as little as six inches in length can mean driving through a brain dead easy to a terribly exciting exercise. When attending a training program, ask the instructor – why are the cone separated by that distance? If the answer is because that’s where the orange dots are you have problems.


The purpose of placing a student in a given exercise or scenario is to evoke a response from the driver/vehicle which introduces or reinforces specific skills or skill sets, and to allow coaching the student on applying those skills and, of course, measure their baseline performance and quantify their improvement. None of this can be accomplished without an understanding of the science of driving which produces the science of designing driving exercises.

These are some of the questions that a professional driving instructor must answer:

  • How far apart are the cones in the slalom?
  • What is the width of the barrier in the lane change?
  • What is the maximum capability of the student’s vehicle, measured in G’s? If you don’t know what the car can do, how can you know what the student can do?
  • What is the maximum rate of de-acceleration of the vehicle? If you don’t know how quick the car can stop, how can you know how quick the student can stop it.
  • At what speed does the student approach the vehicle’s maximum capability in each exercise (or scenario) that you place them in?

If you have an interest in going much deeper into these types of topics, I invite you to check out the International Security Driver Association’s website ISDACenter.Org and consider joining the membership to gain access to the encyclopedia of executive protection and secure transportation – The ISDA knowledge center.

The knowledge shared encompasses a wide range of executive protection and secure transportation-focused topics with resources, information, and metrics.

For more information on all of the member benefits, head over to https://isdacenter.org.

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