How Vehicle Crash Tests Help Make Cars Safer

Intentionally crashing new vehicles helps keep roads and drivers safer.
Trevor English

Ever since the passing of the Highway Safety Act in 1970, which established what is now the US National Highway Traffic Safety Administration (NHTSA), vehicle crash testing has slowly become a vital component of new car production.

It might surprise you that it took this long for mandatory federal safety standards to be established for the automotive industry. With the first cars produced in the early 1900s, it was nearly 80 years before the federal government began rating cars for safety.

In fact, it took even longer in other countries, with Australia, Japan, and Europe all founding their federal automotive safety agencies in the mid-1990s. 

Rating automobiles for how well they perform in crash-tests is generally considered a good thing, though, and helps to make cars safer. In the case of crash testing. the NHTSA acts as an independent rating agency, conducting a variety of crash testing on cars and rating their performance to allow consumers to make informed decisions about the cars they drive.

So, how does intentionally crashing a car actually make cars safer? The answer is twofold: it forces automakers to strive for better safety and better safety ratings, and it provides an abundance of data to help them engineer safer cars.

How crash tests are conducted

In order to understand how vehicle crash tests make cars safer, the first step is understanding exactly how the tests are conducted in the first place. 

Notably, vehicle crash tests don't just include crashing a car, rather there are highly complex crash test dummies that sit inside of the car collecting data about how humans of varying sizes would react to given crash scenarios. These dummies' jobs are to serve as a stand-in for potential future human drivers. 

Prior to standardized crash tests, vehicles were sometimes only found to be unsafe in crashes after many people died. One of the best examples of this was the Ford Pinto, which tended to explode if its gas tank was ruptured in a collision. The Pinto was released in 1970, after the NHTSA was founded, but before crash testing became standard or independently reviewed. After a number of deaths, the NHTSA ultimately told Ford they needed to recall the cars. 

Coming back to the present, crashes and crash dummies are standardized, ensuring that data can be examined in comparison to other vehicles. 

In frontal crash tests in the US, a dummy called the Hybrid III dummy is generally used. These dummies are filled with sensors and built with materials that mimic the consistency of human tissue. These crash dummies aren't cheap either, with each one coming in between $100,000 and $500,000 USD.

Before you scoff at the price tag and perhaps think, "Hey, I'd get in a car crash for $500K", remember, these dummies are reusable and can be crashed thousands of times. Even more so, the complexity of the dummies is impressive, with each having spines made from alternating metal disks and pads, with sensors embedded to measure forces. 

Your spine doesn't have sensors.

While dummies are standardized, they do come in different standard sizes to represent children, toddlers, babies, large people, and small people. After all, people are diverse, so crash test dummies need to be as well. 

As for the sensors, each one has three main types: accelerometers, load sensors, and motion sensors.

How Vehicle Crash Tests Help Make Cars Safer
Vehicle after crash test. Source: Wikimedia/Brady Holt

Accelerometers measure motion in a given direction. These measurements are vectors (values with assigned directions) that allow researchers to closely model the forces at play in an accident. The human body has maximum accelerations, or G-forces that it can sustain in certain locations, so measuring peak acceleration through the accelerometers can be used to determine whether a crash test dummy would've died or not. 

Load sensors measure the amount of force on different body parts. If you think back to physics class, force is mass times acceleration, and the forces at play in a crash are ultimately what will cause injury. 

Movement sensors measure the deflection of the dummies. For example, how much the chest of a dummy compressed during the crash. After crashes are complete, dummies may look fine to the casual observer, but these deflection sensors allow researchers to determine how bad it got for the dummy during the crash, and whether a real human would have been injured.

Enough about dummies though, what about the crashes?

The NHTSA conducts three main vehicle crash tests for new cars: the 35-mph frontal impact and the 35-mph side impact test. 

The frontal impact test involves ramming the car into a concrete barrier at 35 mph. The side impact involves hitting the car with a 1.5-ton sled on its side. This test simulates a car being t-boned or side-swiped at 35 mph.

In addition to these two main tests, there are also side-pole impact crash tests and rollover resistance tests. 

The side-pole test simulates if you were to hit a hole with your car. This is necessary, as the loading in this kind of impact is very focused, meaning that vehicle components in the line of the forces are under some of the highest stress. 

Finally, rollover resistance is pretty self-explanatory. The vehicle is propelled at 55 mph on its side and stopped suddenly. Then, how much the vehicle tips or rolls influence the scores of the car.

Crash test researchers don't just rely on data from the dummies though, the tests are also recorded on a variety of high-speed cameras. Each test is generally recorded on 15 different high-speed cameras all shooting at 1,000 frames per second. 

So, with all of this data that's gathered on vehicle crashes, how is that actually translated into safer cars? One of the ways is by developing better crumple zones into vehicles on the part of the manufacturers. 

Better automotive engineering

Data enables engineers to make better decisions and design better parts. Data in the automotive space allows engineers to design better crumple zones, also known as crush zones. 

When it comes to vehicle crashes, you don't actually want the vehicle to come out of the crash in the best shape possible. Rather, you want the vehicle to deflect, deform, and absorb all the forces in the crash so that those high forces aren't deflected into your body, where they will cause damage. 

If you take a look at old cars, they were basically solid bricks that didn't deflect or deform. This is great for the survivability of the car after the crash, but not so much so for the survivability of the passengers. 

All of this ties back to simple physics. If a car is moving at 50 miles per hour and suddenly stops, all of the things inside of the car will keep moving at 50 miles per hour unless acted upon by an outside force. An object in motion will stay in motion unless acted upon by an outside force - like a brick wall or another car.

This includes your internal organs, your bones, and more. The key to taking this deceleration safely is to increase the amount of time that it takes to slow down. For example, if you're moving at 50 miles per hour, if you slow down in 1 second, you've just decelerated at a rate of 73 ft/s2 (50 mph = 73 ft/s divided by 1s). However, if you take 5 seconds to slow down from 50 mph to 0, your acceleration decreases significantly, to 14.5 ft/s(73 ft/s divided by 5s).

This lower acceleration means lower forces on your body (remember, Force = mass x acceleration).

How Vehicle Crash Tests Help Make Cars Safer
Crash test crumple zone simulation & graphs. Source: EHA/Wikimedia Commons

This longer time to decelerate can be partly accomplished with crumble zones, and it helps save lives. By collecting data from crash tests, engineers can precisely design crumple zones to handle various loading scenarios. 

So what are these crumple zones? They're essentially segments of the frame of the vehicle or of the body that are specifically weakened so that they collapse in a collision. This might involve a small cut in the frame or a small cut in a body panel.

While this might seem counterintuitive, it's all about getting the vehicle to crumble and crack in the ways that will help deflect the force of an impact. Unplanned deformation is bad in vehicle crashes. When engineers can plan for a vehicle to crash in a certain way, they can ensure that the occupants will remain safe. 

Crash test improvements

So, what's next for crash testing? Well, one big change over the last several decades is the expansion of where airbags are placed in vehicles. These new additions to the vehicles are making them significantly safer as they provide soft padding to lower the forces on occupants. 

One of the biggest advancements in airbag tech is actually to make smart airbags. These airbags can sense when to deploy in certain crashes or at certain speeds. This would ensure that the airbags don't just go off randomly or all at once, but rather that they are deployed at the exact right time. 

As for the crash tests themselves, they have slowly evolved over the last several decades. The largest improvements around these tests have simply been the collection of more and more data. More data, like most things in the world, allow better decisions to be made on the engineering and design front. 

This data is also enabling other manufacturing innovations, like smart seatbelts that can adjust tension and force on the fly to protect occupants.