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Driver Safety – It’s More Than Just Vehicle Design

February 22, 2010

After writing my article on the Insurance Institute for Highway Safety’s 50th anniversary crash test, I got some feedback that there is still a community out there that does not believe that vehicle design improvements are the major reason drivers deaths have decreased over time. The crash test did demonstrate the vehicle design aspect of driver safety in a dramatic way, but there are other factors that contribute to increases in driver safety, including public education campaigns and roadway design strategies. How much of a contribution does each factor make? Turns out there’s a study for that. . .

In 2006, the Insurance Institute for Highway Safety (IIHS) website published “Trends over time in the risk of driver death: what if vehicle designs had not improved?” by Charles M. Farmer and Adrian K. Lund. The full text of the article is available here (subscription required). For more about the IIHS itself, see the 50th anniversary crash test post.

What this article concludes is that driving fatalities decreased steadily from 1985 -2003 (see the dark line in the graph below) but potentially for different reasons during different time periods.


The graph below is figure 5 from the research article. You can see it has two lines. The dark, solid line with the filled circles is the actual driver death rate per million registered passenger vehicles from 1985 – 2003. Putting the numbers in per million registered vehicles evens out changes in the number of cars on the road over the 22 year period. Remember the study was done in 2006, and the last available data that year was for 2003, so we can’t make conclusions past 2003 based on this study. This graph shows that actual driver death rates declined steadily over the 22 years in the study. The lighter, dashed line with the empty circles is the death rate that one would expect if design changes had not been made to cars in the years following 1985. That is, if all the new cars on the road today were just like new cars built in 1985, no extra safety features, no additional vehicle types (like SUVs), no design changes to improve crash-worthiness.

Interpretation and Conclusions

Notice the three distinct parts to this graph. In the first section, 1985-1990, the two lines follow each other almost exactly. This suggests that the number of driver deaths was declining, but at a rate that suggests that increases in vehicle safety were not the major cause of the decline. The authors suggest that the main reasons for the decline in driver deaths during this time were behavioral (an increase in safety belt use and increased awareness of the dangers of drunk driving were two factors cited by the authors) and environmental (an increase in traffic congestion leading to slower speeds on roadways and therefore fewer high-speed crashes in urban areas).

graph of data from Farmer and Lund

Driver death rates per million registered passenger vehicles and expected rates based on the 1985 vehicle fleet.

From 1990-1997, driver deaths continued to decrease. Unfortunately, driver fatalities were actually greater that one would expect based on the 1985 vehicle design standards. Why? Weren’t cars supposed to be getting safer during this time? The authors of the study point out that cars were subject to increasing safety standards, but in a push to make them cheaper and more fuel-efficient cars were also getting lighter. According to the authors, “in 1985, the average car weighed 3,005 pounds, compared with 2,838 pounds in 1993.” The authors also point to the rise in popularity of SUVs in the 90’s, and how early SUVs were more likely than cars to roll over, creating a more serious crash situation. Also contributing to more dangerous crash situations, the authors point to the lifting of the federally mandated 55 mph speed limit in 1987, which lead to state laws allowing drivers to go as fast as 75 mph on some roads (higher speeds = more fatalities in crashes).

Fortunately for drivers, in the late 90’s actual driver fatalities continued to decline, and beginning in 1998 the actually number of fatalities dipped below what would have been expected if cars were built the same way they were in 1985. The authors suggest that the dip below expected levels signifies that vehicles are safer now than they were in the 1980’s and 90’s. They cite the fact that average vehicle weight has increased from 2,838 pounds in 1993 to 3,383 pounds in 2003. The authors also cited increased safety standards for SUVs and minivans, both still popular with American drivers but now less likely to roll over under certain crash conditions. Interestingly, you can see the dashed line begins to trend upward in the early 2000’s. The authors interpret this to mean that without design changes that increased vehicle safety in the late 90’s and early 2000’s, drivers would be increasingly less safe on the roads. What factors are creating these unsafe conditions? The authors do not give suggestions, so maybe we can fill in with some speculation of our own. Is driving less safe than in the late 90’s, and if so, why? Will driver deaths continue to decline in the coming decades, or is there something that will cause them to increase? If another study like this comes out, it would be interesting to see if our predictions are actually supported by the data.

So those of you who contend that cars are not as safe as they were back in the day, you have a point. If someone is driving a vehicle from the 1990’s, it probably does not have the same safety features as a newer car. But even if you are driving a newer car, it is no substitute for safe driving behavior like wearing a seatbelt, keeping a safe speed and not drinking and driving.

  1. Just read it and went gosh, I know why I was poor in the debate class. – If builders built buildings the way programmers wrote programs, then the first woodpecker that came along would destroy civilization. Attributed to Weinberg’s Second Law

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