FEATURE ARTICLE
Safer Vehicles for People and the Planet
Motor vehicles contribute to climate change and petroleum dependence. Improving their fuel economy by making them lighter need not compromise safety
Thomas P. Wenzel, Marc Ross
Bad Cars or Bad Drivers?
Our analyses show clearly enough that SUVs and trucks pose considerable dangers, but some of our other findings appear to have less to do with size, weight or design, and more to do with who tends to drive a particular vehicle and how. To probe these issues, we used information about age and gender, as well as various measures of illegal driving (alcohol or drug involvement, driving without a valid license or reckless driving in the crash, as well as the operator's driving record for the previous three years). And although we can only offer some suggestive observations rather than concrete conclusions, certain patterns seem obvious enough to explain why one vehicle so often proves less dangerous than another.
For example, the safest vehicles (for the person sitting behind the steering wheel) are minivans; the riskiest are sports cars. Minivans have the lowest fraction of driver fatalities that are men under 26 years old (4 percent); sports cars have the highest (39 percent). So we suspect that differences in the behavior of their drivers account in large measure for why these two classes of vehicles pose such different risks to the people who operate them. After all, minivans are often used to transport children and, as a consequence, their drivers tend to be especially careful, whereas the people who zoom around in sports cars are likely to, well, cut corners in that regard.
We found also that driving imported luxury cars carries extremely low risk, for reasons that are not obvious. Such cars typically have the newest safety technologies, so perhaps the presence of side-curtain airbags and electronic stability controls contributes here. But curiously, the relatively small number of driver fatalities arising from this class of automobile contains a sizable fraction of young men (21 percent). Assuming that this number just reflects the proportion of imported luxury cars driven by young men, we would conclude that vehicle design and safety features offset the risky nature of many of their drivers.
Smaller cars provide further evidence for this phenomenon. On average, the high-risk subcompact cars we identified appear to be driven by young men only slightly more frequently (23 percent) than are low-risk subcompact cars (21 percent), which suggests that factors other than the characteristics and behaviors of their drivers are causing the large difference in fatality rates. We believe that the details of the designs of these cars make them dangerous.
Another thing we learned was that the drivers killed in SUVs and pickups are no different, at least in terms of age, gender, and driving history, from those of most cars. Therefore, the comparatively high rollover risk and the risk to others we found for SUVs are probably not caused by the behavior of their operators. But we hesitate to ascribe the increased risks in pickups entirely to their design. Why not? Because pickups tend to be driven on rural roads to a greater extent than are cars and SUVs, and such roads are particularly dangerous, for a variety of reasons: They are often designed for lower speeds, but speed limits are rarely enforced; oncoming traffic is not typically separated by a barrier; shoulders rarely have guardrails, are usually narrow and sometimes don't exist at all; these roads are not as well lit; they are often far from trauma centers; and so forth.
To test whether these factors are truly at play, we calculated the population density of the county in which each crash took place. As expected, pickup fatalities occur, on average, in much more rural areas than do the deaths in cars or SUVs. An analysis we did of traffic-accident data from California by county also indicates that, for all vehicle types, fatality risks both to drivers and to drivers of other vehicles increase as population density decreases. Therefore, some of the high risk to others that we calculate for pickups comes from their traveling much of the time on dangerous rural roads, rather than purely from the aggressivity of their design.
To take things one step further, we also calculated risks for individual makes and models. And here we found some very interesting results. For instance, the lowest risk subcompact car, the VW Jetta, appears often to be driven by the most risk-prone drivers: 32 percent of them are young males, many with poor driving histories. Another telling example is the Hyundai Elantra. It had side-curtain airbags added for model year 2001, and we see a 30-percent reduction in risk to Elantra drivers after its redesign, which coincided with an improvement in its frontal crash-test rating, from three to five stars. Similarly, the Ford Focus has a nearly 40-percent lower risk to its drivers than the model it replaced, the Escort. Because the average driver of these models likely did not change much in such a short time period, these reductions suggest that vehicle design can indeed have a large effect on safety.
So how does the fatality risk of car models correlate with their masses? Not as well as one might be led to believe. Other attributes, such as vehicle make, correlate more strongly with fatality risk. In particular, Japanese and German cars have better safety records than U.S. or Korean cars of similar weight. And a car's resale value after five years of ownership is much more strongly correlated with reduced fatality risk than is mass. This observation provides yet more evidence that smart (dare we say "intelligent") design can overcome any disadvantage that lower mass may impart in certain types of crashes.
» Post Comment