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In the World of Cars, Is Bigger Always Safer?

When it comes to cars, is it true that bigger is always better…and safer? Based on an April 2009 study by the Insurance Institute for Highway Safety (IIHS), the answer to this longstanding question is a resounding yes. The study shows that larger, heavy-duty vehicles are fundamentally safer than smaller, lightweight cars.

Considering recent announcements, this revelation is more important than ever. This May, President Obama unveiled his massive fuel efficiency plan. Under the new standards, auto makers will be ordered to increase the fuel economy of vehicles sold in the U.S. to 35.5 miles per gallon by 2016. This means manufacturers will have to produce smaller, more lightweight, fuel-efficient vehicles.

While supporters of the plan say it will help cut our nation’s greenhouse-gas emissions, opponents argue that the mandate will result in thousands more Americans dying or becoming seriously injured in auto accidents. Critics say that the number of auto fatalities could swell if hordes of “unsafe” subcompacts hit the road in coming years.

The physics behind car crashes

Why are bigger cars intrinsically safer? It all comes down to physics. According to the IIHS report, “These tests are about the physics of car crashes, which dictate that very small cars generally can’t protect people in crashes as well as bigger, heavier models.”

Based on the law of physics, when a large object crashes into a smaller object, the larger object creates a greater impact. This rule holds true for car crashes, as confirmed by the IIHS study.

For this study, the IIHS conducted three front-to-front crash tests, each involving a microcar or minicar colliding with a midsize model from the same manufacturer. The Institute did not use SUVs, pickup trucks or even large cars to pair with the micros and minis in the tests. “The choice of midsize cars reveals how much influence some extra size and weight can have on crash outcomes,” the report explains.

Instead, the Institute chose pairs of 2009 models from Daimler, Honda and Toyota because these auto makers have micro and mini models that have earned good frontal crash ratings in barrier tests.

According to the final IIIHS report, “In a collision involving two vehicles that differ in size and weight, the people in the smaller, lighter vehicle will be at a disadvantage. The bigger, heavier vehicle will push the smaller, lighter one backward during the impact. This means there will be less force on the occupants of the heavier vehicle and more on the people in the lighter vehicle. Greater force means greater risk, so the likelihood of injury goes up in the smaller, lighter vehicle.”

Real-world car crash statistics confirm this theory. In 2007, the death rate in 1 to 3-year-old minicars involved in multiple-vehicle crashes was nearly twice as high as the rate in large cars.

Good engineering makes a difference

Despite the recent IIHS study, some experts point out that vehicle safety doesn’t come down to car size alone. They say that quality engineering and design are more important to vehicle safety than the actual car size. Added safety features, such as front and side airbags, seatbelts with pre-tensioners and force-limiters, rollover prevention mechanisms, head restraints and crash avoidance systems can also greatly improve a vehicle’s safety.

Experts also say the size of a vehicle’s front end can determine how the car fares in crash. If a lighter vehicle is engineered with a large front end, creating a bigger space between the front of the vehicle and the front seat, the car would be much safer. That’s because a car with a large “crush space” decreases the severity of an impact and reduces the force to the car’s occupants.

Plus, auto makers can also reduce a vehicle’s weight without losing too much structural integrity by using aluminum, titanium or plastic. Unfortunately, most manufacturers steer clear of these materials because they carry a high price tag.