Episode 181 – Perception of Speed in Motorcades

This week’s topic is the perception of speed in motorcades (e.g. two-car motorcade scenario), and training.

The ISDA 2019 Executive Vehicle Survey results indicated a dramatic increase in the use of SUVs for Executive Transportation. The results also showed that there had been a significant increase in the use of two car scenarios for Secure Transportation services. If you couple the Survey results data with the number of motorcade incidents that have occurred, it points to a problem in the making.

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The following is an explanation of why a motorcade scenario can create a risk to the principal and some suggestions on how to mitigate that risk. The risk starts with what scientists call “driver’s eye height.”

The Driver’s Eye Height

Motorcade Driving

In his book Traffic, Tom Vanderbilt discusses why drivers unknowingly drive faster than they think they are. The information was taken from two studies.

A Drivers Perception of Speed 

The first study was on the perception of speed. The research found that the “average” driver is 15% off; they drive 15% faster than they think they are driving. So, if you think you are driving at 40 MPH or 64.5 KPH, you are more than likely driving 46 MPH or 74 KPH. If you think you are driving at 60 MPH or 96.6 KPH, you are probably going 69 MPH 111 KPH. And the higher you sit in the vehicle, the worse it is. This issue has implications in training. As a trainer, you need to be cautious of the speed in SUVs and monitor them carefully. A radar gun is mandatory. More later in the Podcast.

To carry this one step further, an increase in speed of 15% would represent an increase of 30% in the energy the driver will need to manage in an emergency maneuver and an increase of 30% in the distance required to stop.

The second study was conducted to assess drivers’ chosen speeds when operating a simulated vehicle, doing so while viewing the road from a low eye height, which would be the case if the lead vehicle were a sedan, and a high eye height if an SUV is the follow vehicle).  Participants were instructed to drive, without reference to a speedometer, at a highway driving speed at which they felt comfortable and safe. Drivers seated at a high eye height (the follow vehicle) drove faster than when they were sitting at a low eye height (the lead vehicle).

Our Survey results indicated that the majority of follow vehicles are SUVs and that the seat in a typical SUV is about 1.6 feet/.5 meters higher than in a car. Apply this theory to a two-car scenario where the principal is in a sedan (the driver sitting at normal eye height), and the follow car is an SUV with the driver seated at an elevated eye height. If both drivers perceive that they are moving at the same speed – for example, they both feel they are driving at 40 MPH/ 64.4 KPH due to the eye height of the driver in the follow car, he/she will be driving faster than the driver in the principal car. According to the study, the follow car’s speed can be off by as much as 15%. So, if the driver in the follow car thinks they are driving 40 MPH/ 64.4 KPH, they are more than likely driving 46 MPH/74 KPH. If the driver in the follow car thinks they are driving at 60 MPH/96.6 KPH, they are probably going 69 MPH/111KPH. Also, the higher you sit in the vehicle, the higher the speed differential.

All this leads to the fact that driving the follow car is not easy; following distance will vary and require the driver’s constant attention.

Some thoughts on the two-vehicle scenario:

  1. The driver of the follow vehicle needs to be cautious of their speed. Lots of consideration needs to be given to who is driving the vehicle; putting a driver with little or no experience driving the SUV follow vehicle in a motorcade is problematic.
  2. Preliminary data from the 2019 Executive/Security Vehicle Survey results indicates that the most often rented vehicle is an SUV driven by a subcontracted security driver when traveling. We suggest that the driver has experience driving SUVs and is aware of the misconception of speed that an SUV creates.
  3. There is a substantial difference between the handling capability of the lead vehicle (if a sedan) and the handling capability of the follow vehicle (if an SUV). The difference in handling capability, when coupled with the misconception of speed created by the follow driver’s eye height, can create a significant risk. The driver of the lead vehicle must be aware of their cornering speed. They need to understand that the follow car may not be able to corner at the same speed as the lead vehicle. They need to coordinate their movements. This can be accomplished by advancing the route, and of course, training and practice.
  4. Be cautious of the difference in stopping distance between a sedan and an SUV. A Scenario: the lead vehicle is a Mercedes S 550, which can stop from 60 MPH/96.6 KPH in 128 feet. The follow-vehicle is a Suburban LTZ which can stop from 60 MPH/96.6 KPH in 138 feet/42 meters. The Mercedes comes to a quick stop. The Suburban driver could be moving at the elevated eye height at 69 MPH/111KPH and take 30% more distance to stop the vehicle, so not accounting for reaction time the Suburban would need about 179 feet/54.6 to stop the vehicle. If the driver of the follow vehicle is reacting to the brake lights of the lead vehicle, and considering an average reaction time of .75 Seconds, there would be an additional 76 feet/23.2 meters added to the stopping distance, which would make the total stopping distance 255 feet/77.2 meters – which would present a problem.

Motorcades and Cornering

If we assume that the Mercedes S 550  handles at .85 G’s, which means it can absorb 85 % of its weight, pushing on its Center of Gravity.

The suburban handles at .75 G’s, which means it can absorb 75% of its weight before life gets exciting.

If the motorcade enters a typical 90-degree corner at 35 mph, the Mercedes would be using approximately 80% of its capability. At this speed, an above-average security driver should have the ability to use 80% of the vehicle’s capability.

But if the Suburban driver attempts to follow the lead car at that speed through the corner, we have a problem. The speed of 35 MPH or 56 KPH would represent more than 100% of the Suburban capability.

If the Suburban attempted to follow the lead vehicle through the corner at the same speed, the Suburban and its driver and occupants would be in a loss of control scenario.

To make it more exciting, if we take into consideration the eye height of the driver of the suburban and the driver thinks they are moving at the same speed but are moving 15% faster, which would bring the speed up to 40.4 mph or 65 KPH the Suburban would be 16% over its capacity. Nothing good is going to happen

That’s why motorcade training should require vehicles that are similar in characteristics to those used in the mission.

It is important to know the handling and braking characteristics of the operational vehicles.

When conducting motorcade training measuring speed with a Radar Gun is imperative.

Also, with the technology that is available today for very little investment, the trainers should have all the vehicles equipped with G Meters.


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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