Safer vehicles by redesign

The technical discussion titled "Vehicle Design and the Physics of Traffic Safety" by Marc Ross, Deena Patel, and Tom Wenzel (PHYSICS TODAY, January 2006, page 49) is largely devoted to protecting the occupants of an automobile during an accident. Little is said about designing the car to help prevent the accident in the first place.

The article did mention poor road design and, briefly, driver error; it also referred to a vehicle's center of gravity as a potential problem, particularly if the driver needs to swerve to avoid a collision. However, one big factor not covered is poor car design—in particular that of sport-utility vehicles, which are extremely dangerous to oncoming drivers at night.

The headlights of SUVs and popular pickup trucks are at such a height that they shine directly into the eyes of oncoming drivers. The few seconds of blindness means loss of control by the oncoming driver, and the result may be to drive near or over the edge of the road. The SUV driver may continue on, never realizing that his lights caused the accident. When the police arrive and examine the overturned sedan and injured passengers, they check for alcohol and drugs. If no such evidence is found, they still blame the driver for being asleep at the wheel or suffering a lapse in judgment.

When an SUV and a sedan collide head on, the SUV's high bumper destroys the front end of the sedan and slams the engine into the driver's lap. The characteristic design of an SUV—with higher headlights and a higher bumper—makes it a dangerous vehicle that should be removed from the market.

The good article on vehicle design and safety mentioned various innovations in the continuing effort to reduce traffic deaths. The best solution, of course, is one that prevents accidents rather than just reduces the severity of injuries. One contributing factor to the better Canadian statistics shown in the article's figure 2 is the mandatory use of daytime running lights in Canada. For 20 years or more, headlights that turn on with the ignition have been required on all new cars sold in Canada, wherever they were made. In daylight they operate at a low power; in twilight or darkness they switch to full power. They greatly improve the visibility of approaching cars in dim light or poor weather, and they were generally credited with a reduction of 10% to 15% in the frequency of collisions when they were introduced. My car is six years old and I have never turned the lights on or off and don't know how it could be done. I switch between high and low beams at night, but the automatic controls handle everything else. They even brighten the lights if I enter a tunnel for more than a few seconds.

Ross, Patel, and Wenzel reply: These two thoughtful letters illustrate the importance of myriad details of vehicle design to dangers and safety in traffic. The height of the lights of most SUVs and trucks, which temporarily blind car drivers at night, is a significant risk (which has been crudely quantified in fatality statistics as around 100 per year). Ian Halliday's comments about daytime running lights are indirectly supported by the impressive fatality reductions that are being achieved in Canada (see figure 2 of our article). Those reductions should inspire Americans to question the less-than-impressive claims of success made for US traffic safety programs.

Vehicle design is critical to traffic safety. Specific design features, such as the heights of car seats versus the heights of "truck" fronts, where the trucks are merely serving as car substitutes, are among the most important issues for safety design. Differences in vehicle structures are important; but as we argued in our article, the laws of physics do not imply that vehicle mass, as such, is a safety feature. Observation suggests it is relatively unimportant in today's fleet.