205 – Executive Vehicle Safety and Car Specifications

Episode 205 - Executive Vehicle Safety and Car Specifications
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This episode will cover Executive Vehicle Specifications, including H-Point, Vision Line Height, Cargo Room, and how these measurements affect the safety and security of the vehicle occupants. We’ll also touch on another safety topic, advanced driver assistance systems.

As we have said many times, the executive vehicle is the instrument used by the Security Driving and Secure Transportation profession to earn a living. Many of our Association Members are responsible for the selection and eventual purchase of the executive vehicles.

In the next few years, all vehicles, including Executive Vehicles, will be changing at an exponential rate. The Association will be researching those changes and their effect on Secure Transportation Professionals.


In a Secure Transportation market experiencing the rapid increase in SUVs use, visibility and seating height have never been a more scrutinized metric. The seating height measurement is the distance from the driver’s hip-point (which automotive designers call the H-point) to the ground. The H- Point number is a vital vehicle metric for the Secure Transportation community, especially when operating in a two-vehicle scenario. 

Simply put, the H-point is the theoretical location of an occupant’s hip joint in a vehicle’s seat.

The H-point could be considered the starting point when designing an interior because it influences many aspects such as roof height, seating height, collision performance, outward visibility, interior packaging, and even door apertures.

It is determined by using the SAE International engineering organization’s aptly named H-point machine (HPM). The HPM is a plastic and steel human-shaped device that replicates the 50th percentile male. The first issues are engineering’s definition of the 50th percentile male, which is defined as 69.1 inches tall ( roughly 5 feet 10 inches) and weighing 172 pounds. We are not sure if the SAE assumes that females don’t drive.

The lower-leg components are adjustable, ranging from a male 10th- to 95th-percentile lengths. In its J1100 standard, the Society of Automotive Engineers (SAE), which manufactures and sells the HPM, defines dozens of interior measurements. EPA uses the H- Point number to describe vehicle classes, NHTSA uses the number to position dummies for crash tests.

Vision Line Height

The Vision Line Height (VLH) is the measurement from the car’s floor to the top of the windshield. This region is where the driver will be looking when driving and encompasses the dashboard, wheel, and windshield. 

There is a difference between the headroom and VLH. VLH measurements show approximately how high the seat of the car is. This is important to conceptualize as having a position too high or too low can make it difficult to operate the vehicle. 

The VLH can tell how much vision is cut off by the car’s roof compared to the cabin’s height. Comparing these two with headroom can tell you where your eye level might be and whether the roof will obstruct your vision.

Security Drivers and Secure Transportation professionals need to keep these numbers in mind. The best test method is driving the vehicle. If the same person is driving the exact vehicle every day, then determining the vision line height is not as problematic as it is for Secure Transportation providers who may have multiple people driving the vehicle. VLH is important in determining dead zones, areas in front or behind the vehicle obscured from vision. 

The most important result of VLH is something that we have talked and written about in the past, which is the driver’s perception of speed. 

In his book Traffic, Tom Vanderbilt discusses why drivers unknowingly drive faster than they think. 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, and the higher you sit in the vehicle, the worse it is. This issue also has implications in training. As a security driver trainer, you need to be cautious of the speed in SUVs and monitor them carefully.

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. 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 conducted was 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 you were driving a sedan as the lead vehicle in a two-vehicle scenario. 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 which would be an SUV in a two-vehicle scenario (the follow vehicle), drove faster than when they were sitting at a low eye height, a sedan as the lead vehicle.

There is little a driver can do about VLH except be aware of its effect on driving and motorcades. Raising and lowering the driver’s seat changes the driver’s perception of speed.

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 as the follow vehicle in a motorcade is problematic.

We would be neglectful if we did not talk about VLH in protective driver training. If the instructor judges speed while sitting in the passenger seat, their perception of speed could be as much as 15% off. While conducting training, a Radar Gun or On-Board Computer MUST be used to measure speed.

Episode 181 – Perception of Speed in Motorcades

Cargo Room 

How much luggage a vehicle can carry has always been a major concern in every survey we have conducted concerning executive vehicles. We have found that just because the SUV makes the cargo area look big, the cargo volume may not be what you expect. The reason is due to the complex shapes, the door opening contours, it doesn’t really tell you exactly what can fit in one vehicle versus another.

From a safety concern, there is a metric that is important – the Static Stability Factor (SSF). The SSF is how the National Highway Traffic Safety Administration determines a vehicle’s rollover probability. It is the vehicle’s at-rest calculation of its rollover resistance. The number is based on the vehicle’s geometric properties. SSF is a measure of how top-heavy a vehicle is. The more cargo you put in the vehicle that is located above the vehicle center of gravity, the more prone the vehicle is to tipping over. 

The lower the SSF number, the more likely the vehicle will rollover in a single-vehicle crash. A higher SSF value equates to a more stable, less top-heavy vehicle.

What is a good SSF?

NHTSA rates the SSF of a vehicle by using a star system

Five stars: less than 10 percent chance of a rollover

Four stars: 10 to 20 percent chance of a rollover
Three stars: 20 to 30 percent chance of a rollover
Two stars: 30 to 40 percent chance of a rollover
1 star: greater than 40 percent chance of a rollover

NHTSA SSF Vehicle Ratings

Common Executive Vehicles SSF Ratings


So what are the NHTSA SSF Star Ratings for some of the more prevalent Executive Vehicles?

  • Mercedes S Series is five stars or a less than 10 percent chance of a rollover.
  • Lincoln Navigator 4 stars or a 10 to 20 percent chance of a rollover
  • The Chevy Suburban is three stars or a 20 to 30 percent chance of a rollover.
  • A Mercedes Sprinter Van comes in with a 1 star or a greater than 40 percent chance of a rollover.

All these SSF safety ratings are measured when the vehicle is unloaded. If you load luggage into any of these vehicles above the center of gravity, the rollover probability increases.

So, let’s put these numbers in a two-car scenario.

The lead car is a Mercedes S Class, and the follow vehicle is a Suburban. When driving through a corner onto an off-ramp performing an emergency maneuver, the Suburban has more of a propensity to roll over than the Mercedes.

Is this a problem? As long as the vehicle is in the hands of a professional – no, but if the vehicles are driven by those with no training or experience – yes.

Vehicle Safety Ratings

The job of a security driver is to supply safe and secure transportation; hence vehicle safety rating is of importance. The best source of information concerning vehicle safety is National Highway Traffic Safety Administration (NHTSA) and the Insurance Institute for Highway Safety (IIHS).

These two organizations perform crash tests on cars in the United States. The ratings those agencies produce are found on the vehicle’s window stickers and are the standard for vehicle safety ratings. 

 Link in show notes



In addition to vehicle safety ratings, the security driver and secure transportation professional need to look and have knowledge of the vehicle’s active-safety technologies.


  • Most all Executive Vehicles are equipped with a full array of active-safety technology. Here are a few of the more prominent ADAS features and what they do.
  • Forward Collision Warning – Gives visual, tactile, or audible warnings that alert the driver to the possibility of a collision with an obstacle in front.
  • Automatic Emergency Braking – Automatically applies brakes to prevent or reduce impact force in a collision with an obstacle in front.
  • Adaptive Cruise Control – Keeps a constant distance between you and the car ahead, automatically maintaining a preset following distance.
  • Blind Spot Warning – Provides a warning that something is in the vehicle’s blind spot.
  • Lane Departure Warning – Gives warnings intended to alert the driver that the vehicle is crossing lane lines.
  • Lane Keeping Assist – Provides automatic corrective steering or braking to try and keep the vehicle in its lane of travel.

The Issue with ADAS

The issue is every manufacturer has a different name for each of these ADAS features. Of more importance is that not all ADAS systems are equal. They have other methods of alerting the driver of a problem. One system may use a light to warn the driver; another may use a sound system for the same problem. If you drive the exact vehicle, then it is just a learning curve. But it will be a problem in a Secure Transportation Provider scenario where different drivers are driving the same vehicle and are not familiar with the alert systems. This problem has an easy solution. When getting into an unfamiliar vehicle, the professional security driver needs to get familiar with all the ADAS features and their alert notification systems. 

To gain an understanding of ADAS features, we suggest looking at the ISDA’s YouTube Channel playlist devoted to ADAS – we’ll have a link in the show notes.

The ISDA ADAS YouTube Channel Playlist

Autonomous Vehicle Levels 

Another safety issue that is dominating vehicle advertising is the autonomous vehicle levels. Some have touted driverless vehicles on various social media outlets, news reports, and vehicle ads. There is a TV ad that you may have viewed –  it shows a group of people driving while clapping their hands to the music. Basically, driving for a considerable length of time with their hands off the steering wheel is irresponsible but not illegal.

As a Security Driver or provider of Secure Transportation, we are confident that we don’t need to remind you to keep your hands on the steering wheel. 

That is not to say that basic autonomous vehicles are here to stay, and your client or principal is watching the same TV ad. As a Security Driver or provider of Secure Transportation, your client or principal expects you to stay current and know the ever-increasing technologies available in executive vehicles. The various levels of Autonomous vehicles and their effect on the driving task are some of those pieces of knowledge you need to have. 

For additional information, we suggest listening to episode 172  – Autonomous Vehicle Levels and Security Driving.

Join the Association

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 and consider joining the only organization dedicated to supporting the advancement of professional Security Drivers and other protection practitioners with data-driven research and other professional development tools.

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

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