How To Survive a Head-On Collision – Slow Down (to below 43mph)!

To survive a head-on collision, your odds are best below 43 mph.

Lately, I’ve been writing a lot about Vision Zero. It’s an initiative a number of wealthy countries around the world are following to different degrees with the overall goal of reducing auto fatalities in their populations. One of the central tenets of Vision Zero is the belief that roadways need to be designed to protect different kinds of travelers from coming into contact with each other above particular speeds. For example, if you’re an unprotected traveler, like a pedestrian, any roadways you use that might put you in contact with cars (e.g., cross-walks) should not have traffic traveling any faster than 20 mph. These guidelines also exist for individuals traveling in cars who might come into contact with other cars, which is precisely what this article is about.

What can we do to increase our odds of surviving a head-on collision?
To put it simply, if you want to survive a head-on collision, the best way to do so is to avoid getting into one to begin with. But if that’s not possible, the second best way to survive is to drive as slowly as possible prior to the collision–ideally, no higher than 43 mph. More broadly, since collisions are difficult to predict but the roadways we choose are far more likely to be under our control, I’d avoid driving on any undivided roadway with a posted speed limit above 40 mph.
What makes 43 mph the limit for survivability?
The specific figure comes from research related to Vision Zero, such as a Monash University study in 1999. The researchers came up with a series of guidelines related to the highest amounts of violence, or crash forces, the human body could tolerate under certain assumptions (e.g., well-designed vehicles with crash structures, or passengers wearing seat belts) without risks of serious or fatal injuries. For vehicle occupants traveling on roads where frontal impacts were a possibility between cars, they recommended a long term speed limit no higher than 70 kph, or approximately 43 mph.
But I know  / heard of someone who survived a head on at 50/60/80 mph!
While it’s certainly possible to survive frontal crashes at higher speeds, the odds of doing so drop exponentially above this speed. After analyzing dozens of crashes over the last several years, I’ve found survivors of head-on collisions in a range of speeds, but the rate of fatalities has always risen dramatically with the speeds of the collisions, while the rate of survival has always dropped as quickly. Remember that a crash with a 50% survival rate suggests that if you and someone you love are sitting in the front row of a vehicle, statistically speaking, either you or your loved one isn’t going to survive such a collision. Those aren’t the kinds of odds you want on your side each time you drive.
How do other safety organizations (i.e., the IIHS) feel about this figure?
While the IIHS doesn’t specifically advocate 43 mph speed limits, they have repeatedly advocated slower speed limits and bemoaned the rising tide of speed limits throughout the country. Additionally, one of the most direct endorsements of a 43 mph limit for head-on collision survivability comes from the IIHS’ frontal moderate- and small-overlap crash tests. Both of these tests are conducted at 40 mph, and are designed to simulate the effects of a vehicle crashing into a vehicle of equal mass traveling in the opposite direction at 40 mph. They’ve noted that these kinds of crashes are already considered to be “severe” ones, and that tests are not conducted at higher speeds due to the impracticality of designing vehicles capable of protecting occupants at higher speeds.
Does this mean my car / SUV / minivan / pickup is only designed to protect my family at up to 40 mph?
In a head-on collision, yes. This isn’t because car manufacturers don’t care much about keeping people safe at high speeds or that organizations like the NHTSA and IIHS don’t care about things that happen at higher speeds; again, it’s simply a reflection of how much additional energy vehicles carry at higher speeds, and how difficult it is to design vehicles to protect individuals above those speeds because of how energy increases with speed. But once again, when you hear that your vehicle comes with a 5-star frontal crash rating or a “good” frontal impact score (whether head-on, moderately overlapping, or small overlapping), it’s essential to remember that this only applies for crashes at 40 mph, and with vehicles that weigh as much as or less than your vehicle. At higher speeds, there are no guarantees.
How much more severe is a crash at 70 mph than one at 40 mph?

It’s important to remember that the forces in a collision quadruple when speeds are doubled, rather than simply doubling, because kinetic energy increases with the square of velocity. To put this in practical terms, a crash at 80 mph carries 4x the energy as a crash at 40 mph, even though the speed is only 2x as fast. As noted above, your vehicle is only designed to protect you from a crash with an equal or lighter mass vehicle at 40 mph. Let’s use that as a baseline, where your vehicle handles 100% of tested forces while allowing you to survive the crash with minimal injury. At these speeds, your odds of survival in a vehicle with a “good” frontal score are close to (not quite, but close to) 100%.

A 70 mph crash carries more than 2x as energy, or precisely 306% as much energy as the 40 mph crash (100% of tested forces). In my observations from studying crashes, once you get up to around 300% of the forces your vehicle was designed to handle, your odds of survival drop down to around 25%. To put it another way, in a head-on crash at 70 mph involving 2 vehicles with 4 people in the front seats, only 1 of the 4 people involved is likely to survive.

This is the risk we run every time we drive at 70 mph in an environment with a possibility of head-on collisions (i.e., every undivided highway in the country).

If crashes are this much more dangerous above 40 or 43 mph, then why do we have speed limits at 55, 65, or 75 mph?

That’s a great question. A basic answer is because our society (as well as virtually every other around the world) prioritizes speed over safety when it comes to auto travel. Additionally, most people aren’t aware of the dramatically increased risks that come from higher speed limits until it’s too late (you can’t advocate from beyond the grave). However, it’s important to remember, too, that speed limits beyond 43 mph can be tolerated with low risks of severe injury or death as long as the risks of head-on collisions are eliminated, which is possible through good road design. The challenge is to bring that good road design to a country that’s plagued with poor road design.

What do you mean by poor road design?

Poor road design, per Vision Zero, in this context refers to roadways with an opportunity for head-on collisions that permit or encourage vehicles to travel beyond 43 mph. In other words, two-lane undivided highways with 50, 55, or 60 mph (or higher!) speed limits are roadways that shouldn’t exist, but do throughout the US (and globe).

What does this mean for my family and I? Do we have to drive at 43 mph everywhere?

Not necessarily. But as noted earlier, I’d certainly try to avoid driving on any undivided roadway with a posted speed limit above 40 mph. The risk increases exponentially with the speed of traffic. And given the propensity of people to speed in this country, a road with a 40 mph PSL will most likely already be dealing with 45-50 mph traffic. You can do the math for higher speeds.

If you’re about to get into a crash, the best thing you can do in the three seconds beforehand are to slow down as much as you possibly can. If you have the luxury of choosing your roadway, stay away from undivided roads with speed limits above 40 mph. Your life could literally depend on it.

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