February 9, 2020

Mental models

The killer(s) on the road: reducing your risk of automotive death

How, where, and why do most people die behind the wheel of an automobile? Is there anything we can do to prevent deaths on the road?

Read Time 9 minutes

Last week we talked about how we can often conflate the frequency and severity of accidents. We may mistakenly believe that the chances of dying are greater in the air than on the road because the severity of aviation accidents can be devastating. Compare that to automotive accidents where the probability of dying in a given automotive accident is about one half of 1 percent. Here’s the rub, unfortunately: nearly 18,000 automotive accidents occur every day in the US, on average. This frequency multiplied by the low severity still amounted to nearly 37,000 automotive fatalities in 2018. To put this difference into perspective, between 2000 and 2018 there were 778 fatalities from US scheduled air travel. Over the same time span, there were 723,530 automotive fatalities—almost 1,000 times greater than the number of fatalities from scheduled air travel.

These numbers should scare anyone. If I die in the next 10 years, the most probable “murder weapon” is my vehicle or another vehicle on the road. Is there anything I can do to lower the chances of dying in a car or from a car? Of course, never stepping foot in a car again would drastically lower my chances, but there are trade-offs in life. Before I get into my risk-reduction strategy, a few statistics are in order to inform it. Also, a caveat: for this analysis, I’m only interested in the driver and what he or she can do to lower the risk of death. I care a lot about pedestrians and other occupants in the vehicle, but to do this analysis, I must remove them from the equation.

Of all drivers killed in US automotive accidents in 2017, 18% occurred on a freeway. This is actually lower than I expected. I think this speaks to a more controlled environment where an interstate must meet federal standards and includes fully controlled access (i.e., entering and exiting is confined to on and off ramps) and a median width of at least 50 feet.1This control of access importantly requires what is called grade separation, meaning interstates should not have any intersections. Interstates, specifically, account for 13% of driver deaths, while freeway and expressway crashes make up the other 5%. For those wondering about the nomenclature, it’s a little messy, but interstate highways must conform to the most stringent safety standards, followed by freeways (most interstates are freeways) which also include fully controlled access, while expressways may only be partially-controlled; they have a very limited number of at-grade intersections. Despite the differences, for simplicity, I’ll refer to this category simply as “freeway” from now on.

Perhaps the biggest reason why we don’t see more fatal crashes on freeways is that there are no intersections on them (with a few exceptions). In fact, there are more drivers killed in intersections (20%) than on freeways.

After accounting for freeways (18%) and intersections and junctions (20%), we’re still left with more than 60% of drivers killed in automotive accidents left accounted for.

It turns out that drivers killed on rural roads with 2 lanes (i.e., one lane in each direction divided by a double yellow line) accounts for a staggering 38% of total mortality. This number would actually be higher, except to keep the three categories we have mutually exclusive, we backed out any intersection-related driver deaths on these roads and any killed on 2-lane rural roads that were classified as “freeway.” So, to recap, 3 of out every 4 deaths in a car occur on the freeway, at an intersection/junction, or on a rural road with a single lane in each direction.

Let’s double-click on each one of these categories and see if we can answer two very important questions:

  1. What driving error resulted in the fatality?
  2. Who is most likely to be at fault and what was the underlying cause of the error? (One way to think about this question is through the lens of manslaughter versus accidental suicide—was the driver effectively killed by someone else making a mistake, or by a mistake they made?)

If we can answer these questions, we may gain insight into what we can do to lower our risk of death (and the death of others) while driving.

In the cases where drivers are killed on freeways, 31% of them have alcohol in their system and nearly 85% of these drivers were over the legal limit of 0.08 g/dL.  Furthermore, 29% of all driver deaths involved speeding, and just under 1 in 10 involved distracted driving. It’s difficult to get mutually exclusive and collectively exhaustive data here, and there are often multiple related factors. For example, it’s not uncommon for a driver to die on a freeway while speeding and over the legal limit of alcohol.

The primary conditions that lead to fatalities, then, are: alcohol, speeding, and distraction leading to a loss of control or contact with another vehicle.

Who is likely to be at fault on a freeway, the driver that was killed, or another driver on the road? It’s not exactly clear from the data, but that doesn’t change our strategy.

Why? I think the steps below make it clear.

Rule #1: Consider the conditions above as your not-to-do list to reduce the risk of accidental suicide: Do not drive with alcohol in your system, even if you are (or think you are) below the legal limit. Do not speed. Do not text and drive. Do not get behind the wheel if you are sleep-deprived.

Rule #2: Assume others are not adhering to Rule #1. In particular, assume one person awoke today with the explicit instruction to kill you with their car. If you knew this, how vigilant would you be? How much more closely would you pay attention to each other driver around you? That person swerving around or braking too late? That person looking at their phone? That person speeding up behind you? Look for the killer. Be vigilant at all times, and make sure today is not his day.


Let’s move to the next category of fatalities—intersections and T-junctions.

I learned something from one of my best friends in high school who is a long haul truck driver. Talk about someone having a front-row seat to vehicular manslaughter. He told me many years ago that when approaching an intersection, with the right of way, he always looks left first, then right, before entering. Why? The data below show you what his intuition suggested and his experience crystalized.

Let’s start with intersections. A driver is most likely going to be struck near the driver’s side by another vehicle, otherwise known as a broadside or T-bone crash. Figure 1 illustrates the different crash scenarios. If a driver is heading through an intersection, with the right of way, the most common cause of his death is the driver on his left, where both cars cross paths, as scenario #2 in Figure 1 most clearly depicts.

Scenario #5, in which two cars go straight through the intersection, has the highest severity. While the figure shows the vehicle heading left to right struck by the one heading up, it’s often the case where the vehicle heading up is struck by the other heading left to right, running a traffic signal or stop sign.

Figure 1. Schematics of, and percent of fatal crashes, Common Crossing Path Crash Scenarios. Fatal crashes include intersections and T-junctions. Figure from the US Department of Transportation.


(1) Left Turn Across Path – Opposite Direction Conflict (LTAP/OD)
(2) Left Turn Across Path – Lateral Direction Conflict (LTAP/LD)
(3) Left Turn Into Path – Merge Conflict (LTIP)
(4) Right Turn Into Path – Merge Conflict (RTIP)
(5) Straight Crossing Paths (SCP)

Who is most likely to be at fault when a fatal driver crash occurs at an intersection? It’s often the driver that dies who is the one not at fault. They’re more likely to be obeying the rules of the road, with the right of way, when someone blows a stop sign or traffic light and strikes the victim on the driver’s side, or at an angle.

However, the fault is often shifted to the driver in fatalities occurring at T-junctions. In this case, the driver that’s going to be killed reaches the junction (i.e., traveling up the stem of the “T”) where the road intersects, and proceeds to make a turn before it is safe to do so and is most often struck on the left side by the car traveling in the lateral direction (i.e., heading left-to-right on the horizontal line of the “T”) with the right of way. This type of accident resembles scenario #2 in Figure 1. The second most common way to get killed is when traveling right-to-left on the “T” and turning left into the stem of the “T” and the vehicle is struck by another heading in the opposite direction. This accident looks like scenario #1 in Figure 1 (you need to rotate the figure 90 degrees left in your mind’s eye for it to match my “T” description for it).


Lastly, let’s turn our attention to the final, and largest, category of deaths. Determining who’s more likely at fault in driver deaths on 2-lane rural roads may be a little bit harder to pinpoint, but we have some clues. In about 10% of drivers killed in this category, prior to the crash, also referred to as the pre-crash critical event, another vehicle heading in the opposite direction crossed the left lane (i.e., the double yellow line) into the victim’s lane. I think it’s safe to assume that the other driver was responsible for the crash.

However, more often (17% of cases), a driver that is killed on this type of road is the one crossing the lane to his left and encroaching on the opposite lane of travel as the pre-crash critical event. In drivers killed on 2-lane rural roads, 50% involved a driver not wearing a seat belt. Close to 40% have alcohol in their system and nearly 90% of these drivers were over the legal limit of 0.08 g/dL. About one-third involved speeding, and 16% did not have a valid driver’s license. I think this suggests that driver error plays a larger role rather than another driver at fault. At the least, it suggests that there are some simple things we can do to lower the driver death rate. Which brings me to the larger point of this post.

What are some of the things you can do to improve your chances of not becoming a statistic on the road?

The first thing you should do is understand what you should not do.

  1. Speeding is the biggest related factor, involving an estimated 30% of all drivers killed.
  2. Next is being under the influence of alcohol (as well as drugs or medications, the most common being stimulants, that may make drivers more aggressive and reckless, and cannabinols, that may slow coordination, judgment, and reaction times), where 33% have at least some alcohol in their system and nearly 90% of these drivers were over the legal limit of 0.08 g/dL.
  3. After that comes distracted driving (8%), which of course involves the use of mobile phones, failure to keep in the proper lane or running off the road (7%), failure to yield the right of way (7%), and careless driving (6%). I would argue that all of these factors are a form of careless driving (with the exception of some of the crashes involving running off the road).

These are not mutually exclusive factors. I would also argue that the numbers on distracted and drowsy driving (the latter not included above because it’s reportedly involved in only 2% of driver deaths) are underestimated and don’t capture the influence of texting in the case of the former, and the impact of poor sleep in the latter, except in the most extreme cases.

How can you drive more carefully? The best place to start is to look at the factors in the list above and take an honest inventory. As I discussed in the previous email, while there’s no assurance that what I do in a car will keep me alive, I think I can reduce the odds of that happening, beyond simply avoiding these factors, as important as they are. But, and here’s the key point, assume someone like this person is on the road at all times, and his sole purpose is to kill you. He’s a serial killer and uses his vehicle as his murder weapon. His killing statistics eerily resemble the overall fatal crash statistics. He does a lot of his killings at intersections, but isn’t shy about hopping on the freeway and taking people out there, too.

On the freeways, he may suddenly leave his lane and enter yours within inches of your front bumper, or he’s side by side trying to make contact with your vehicle. Be on the lookout for this maniac.

At intersections, he really likes being on your left and he loves running red lights and stop signs. If you’re going through a green light or a road that intersects with stop signs, look left before you enter and cross the intersection. If you’re at a red light that turns green or proceeding through a stop sign, first look left to make sure the killer isn’t there.

On rural 2-lane roads, he’s been known on occasion to travel in the opposite direction of his victim, leave his lane and force his distracted victims, who traveled these roads so many times they think they can drive them in their sleep, into an avoidance maneuver that results in them driving off the road and rolling their vehicle. This is where you need to remind yourself that even though you’ve driven these roads countless times without a scratch, it does not give you a pass to be more complacent and lose your focus.

Remind yourself every day to take these measures every time you get behind the wheel. Most of these are obvious and you’ve heard them before, but if you look at the data, my hope is that it makes the steps you can take more tangible.

Here in Table 1, I summarize the primary locations of US automotive fatalities, the underlying causes, and most importantly, the steps you can take to reduce your risk of succumbing to them beyond the obvious (Rule #1, above, the so-called not-to-do list).

Table 1. Common causes of driver deaths and additional strategies to reduce their risk.

Before closing this morbid email, one of my patients, who is himself a very frequent helicopter passenger, sent me his rules of engagement for safer flying after reading last week’s email. With his permission, I’m listing them here.

  1. Always fly a twin engine. Two engines are better than one. Statistically, yes, and obvious.
  2. Always “try” to get two pilots. Not because one might have a heart attack (also possible) but to help for visual aid. Watch next time you are in the New York harbor. One pilot is always frantically looking around to avoid the heavy traffic.
  3. If on a crowded helicopter – and they don’t weigh everyone – ask why? It’s actually mandatory on the best-run helicopters.
  4. Always ask for instrument capable pilot and guidance systems.
  5. Always try to avoid bad weather with limited visibility.


– Peter

Disclaimer: This blog is for general informational purposes only and does not constitute the practice of medicine, nursing or other professional health care services, including the giving of medical advice, and no doctor/patient relationship is formed. The use of information on this blog or materials linked from this blog is at the user's own risk. The content of this blog is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Users should not disregard, or delay in obtaining, medical advice for any medical condition they may have, and should seek the assistance of their health care professionals for any such conditions.


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