By Mike Simpson, Kristine Chan-Lizardo, Cory Lowe, and Cameron M. Burns
President Obama announced on May 19, 2009, a “historic agreement to help America break its addiction to oil.” The centerpiece of that announcement was a new 35.5-mpg CAFE standard for 2016. Rocky Mountain Institute (RMI) has been advocating the entry of fuel-efficient cars into the market for years. The time is now ripe, and we are in the midst of a major national push for the adoption of these cars.
One of the barriers to widespread adoption is the common-yet-misleading line of logic that most consumers follow—that fuel efficiency equates to smaller, less safe cars.
This misperception is fed by the media, including an April 14 New York Times story, “Study Says Small-Car Buyers Sacrifice Safety for Economy” and a May 22 The Wall Street Journal piece, titled “Light Cars are Dangerous Cars.”
Sure, based purely upon a typical vehicle's design, geometry, and occupant position, we agree that larger—but not necessarily heavier—vehicles can offer considerable safety advantages to passengers within. But left out of this quickly developing story is engineering design.
Recent research by Rocky Mountain Institute indicates that an ultralight vehicle that is large and better designed can have crash safety comparable to, or better than, that of a similarly sized heavy vehicle. The platform of a light and large vehicle relies on stronger, lighter materials. Designing for passive safety on par with current NHTSA five-star ratings demands not only using lightweight materials, but also new vehicle geometries and components that can act as energy-absorbing crumple zones. Indeed, a lighter vehicle can achieve the performance of a conventionally designed vehicle, but because it can do so with a smaller engine, there is more room in the engine compartment for crush space and, ultimately, a better crumple zone design. Furthermore, automobile manufacturers are beginning to incorporate advanced active safety features, such as side curtain airbags, and collision prevention systems, such as Volvo's "City Safety."
There is another aspect of safety not considered when using conventional logic: the safety of the people outside the car. A lightweight vehicle will be less aggressive (less likely to injure the occupants of another vehicle, bicyclists, or pedestrians external to the primary vehicle in a collision), thereby reducing the overall number of traffic deaths. For an object moving at a given speed, a reduction in mass corresponds to a reduction in the amount of energy that object brings into a collision with another object. Thus, a lightweight fleet (traveling at the same speeds) is statistically less dangerous than a conventional (heavy) fleet.
As part of our research on vehicle lightweighting, RMI reviewed all the available data and commentary about the relationship between size, safety, and weight, including reports published by the National Academy of Sciences and the National Highway Traffic and Safety Administration, and the Insurance Institute for Highway Safety (IIHS). Many reports link size and weight as being responsible for safety reductions, while the most recent studies disaggregate the two, and find size alone to blame.
In a January 2007 article, IIHS stated “a way to improve fuel economy and maintain vehicle crashworthiness is to use lighter materials that reduce vehicle weight but not size.” IIHS also noted “Indexing these requirements to the vehicle size makes it less likely that auto manufacturers will reduce the weights of their vehicles in ways that degrade occupant protection, and some weight reduction, especially among very heavy vehicles, could improve total safety by lowering the risk to other people on the road.”
The fact is that today, there are not many examples of vehicles that have been designed to be both lightweight and large. This will soon change as domestic and overseas automakers explore designs and materials that will be both fuel-efficient and safe.
RMI continues to encourage OEMs to make efficient, lightweight cars. We hate to see the benefit that comes from fuel efficiency thwarted by misconceptions about safety trade-offs. Both fuel efficiency and safety can be achieved and both are good for the health of the country in more ways than just safety on the road.
Results of a recent RMI study on this topic are expected to be released in July.
For additional information, please visit www.rmi.org.
The authors are all employees of Rocky Mountain Institute, where Mike Simpson is a transportation analyst, Kristine Chan-Lizardo is Interim Director of the Mobility and Vehicle Efficiency Team (MOVE), Cory Lowe is a public relations manager, and Cameron M. Burns is Senior Editor.
