Would a large Rice Krispie square meet current guidelines for temporary highway traffic barriers?
— Raymond C., Australia
If you’re willing to do the tests to demonstrate it, it really might!
Traffic safety barriers can be made of a lot of stuff. Those yellow barriers you see by the side of the highway are designed to crumple safely during a crash and absorb a vehicle’s momentum. They’re composed of a wide variety of materials, including plastic, foam, water, sand, steel and various honeycomb structures.
Rice Krispie treats are brick-shaped snacks manufactured by Kellogg. A report by the Tariff Classification and Marking Branch, a part of U.S. Customs and Border Protection, describes them as “moist, gooey, sticky, easily malleable, and very sweet like a marshmallow,” which makes me wish food manufacturers were allowed to use only descriptions from government inspection reports in their marketing.
The ability of Rice Krispies to absorb impacts has, surprisingly, been studied in laboratory tests. Julio R. Valdes, an engineering professor at San Diego State University, has conducted several experiments in which Rice Krispies were crushed with a plunger to observe the way the material fractured.
Dr. Valdes said his work focused on the way soils are crushed under pressure, which is important for designing secure foundations for dams, retaining walls and other structures. For one series of tests, he wanted to use a material with grains large enough to be seen easily, but weak enough that they could be crushed in the lab without industrial equipment.
“So I thought of cereal,” he said. “It’s just like a crushable sand. It’s cheap and the grains are weak.”
Dr. Valdes said the cereal’s famous “snap, crackle and pop” also made it easy to detect the collapse of individual grains.
Thanks to his experiments, we can estimate that a volume of puffed rice the size and shape of a typical highway barrier could actually be able to absorb the impact of a speeding car. (Because the cereal’s resistance rises as more grains are crushed, you might need to make the Rice Krispie barrier larger than a regular highway barrier, so the car comes to a stop before it gets too compacted.)
All these estimates are based on lab experiments using dry cereal. But Rice Krispie treats are bound together with a sticky marshmallow substance. This sugary mortar increases their stiffness and density, so it’s possible they would stop a car too quickly, amplifying the damage done to the vehicle and its passengers. Forming the treat into a honeycomb pattern, to space out the impact over a longer distance, might help address this problem.
Because Rice Krispie treats harden as they dry out, the barrier would become stiffer over time. If it met standards when installed, it might become too firm after just a few days exposed to the elements.
Dr. Valdes remains skeptical. “If you were to ask me, based on what I know, whether Rice Krispies would work as a crash barrier. …” He paused. “It’s still an open question.”
Fortunately, our safety doesn’t depend on these theoretical calculations. To get a new device approved as a safety barrier, you’ll need to conduct real-world crash tests.
Even if your Rice Krispie treat barrier gets approved, you might want to think twice before deploying it. Anyone who’s had a picnic outside knows that sugary snacks are a magnet for hungry insects. The barrier might keep you safe during the crash … but introduce new dangers after.