Killer Cars: An Extra 1,000 Pounds Increases Crash Fatalities by 47%

Photo: AFresh1

Ever since the SUV craze began in the late 1980s, we’ve all known that heavier vehicles are safer for those driving them, but more dangerous for others on the road. Which is why we all started driving them. Now, in a new working paper, a pair of Berkeley economists have quantified not only the fatality risks of heavier cars for other drivers, but also the costs associated with them. Here’s the abstract:

Heavier vehicles are safer for their own occupants but more hazardous for the occupants of other vehicles. In this paper we estimate the increased probability of fatalities from being hit by a heavier vehicle in a collision. We show that, controlling for own-vehicle weight, being hit by a vehicle that is 1,000 pounds heavier results in a 47% increase in the baseline fatality probability. Estimation results further suggest that the fatality risk is even higher if the striking vehicle is a light truck (SUV, pickup truck, or minivan). We calculate that the value of the external risk generated by the gain in fleet weight since 1989 is approximately 27 cents per gallon of gasoline. We further calculate that the total fatality externality is roughly equivalent to a gas tax of $1.08 per gallon. We consider two policy options for internalizing this external cost: a gas tax and an optimal weight varying mileage tax. Comparing these options, we find that the cost is similar for most vehicles.

Some highlights:

From 1975 to 1980, average vehicle weight in the U.S. dropped almost 1,000 pounds, from 4,060 lbs to 3,228 lbs. By 2005 those reductions had all been gained back, and the average car was as heavy as it was in 1975.

Previous research has suggested that a heavier car fleet is a safer one. This study concludes that tightening fuel economy standards (and thereby reducing the weight of cars on the road) will not increase fatalities, so long as the standards are “footprint based” or unified across cars and trucks. Here’s how:

We quantify the external costs of vehicle weight using a large micro data set on police-reported crashes for a set of 8 heterogeneous states. Unlike the data sets employed in the previous transportation literature or Jacobsen (2010), our data set includes both fatal and nonfatal accidents. Using unique vehicle identifiers (VINs), we determine the curb weight of each vehicle involved in an accident, thereby minimizing concerns about attenuation bias induced by measurement error. The rich set of vehicle, person, and accident observables in the data set allow us to minimize concerns about omitted variables bias. Using these data, we estimate the external effects of vehicle weight on fatalities and serious injuries conditional on a collision occurring.

Two key results emerge:

1. That vehicle weight is a critical determinant of fatalities in other vehicles involved in multi-vehicle collisions. The data implies  that a 1,000 pound increase in striking vehicle weight raises the probability of a fatality in the struck vehicle by 47%. The authors then calculate that the total external costs of vehicle weight from fatalities alone are about $93 billion per year.
2. Second, light trucks significantly raise the probability of a fatality in the struck car – in addition to the effect of their already higher vehicle weight.


Peter St Onge

I think you missed the two interesting economics questions here.

First, this is a classic public goods question - heavier cars might create more fatalities but they are safer for their driver, who can transfer risk to other drivers. Since the driver is the decider on how many SUV's are on the road, it's a nice illustration of externalities.

Second, you put the blame on "heavy" when, logically, the blame lies with "inequalit." If everybody drove SUV's this damage would be mitigated, no? Meaning the blame also lies with small-car drivers, just as it would if they didn't wear their seatbelts.

James

Except that you also need to include the externalities (and internalities, if that's the right word) of such things as fuel consumption and driver attitude & involvement. Fuel consumption's pretty obvious: I see it in action every month or so, when I put $20 worth of gas in the hybrid, and watch the SUV owners on the other pumps run up close to 3 figures - and know they'll be back next week.

It's the attitude thing that I think really causes the problems. SUVs and the like are so big that many of their drivers appear to believe that they're exempt from all sorts of constraints, ranging from common courtesy to the laws of physics. They're so insulated from the world that their drivers feel free to use them as mobile office, gossip fest, makeup parlor, and sometimes video game center.

Caleb b

"There’s no reason you can’t add the taxes for the external costs of larger vehicles while still working to reduce the other risk factors."

Just a thought, by your logic I could also tax smaller vehicle owners for putting themselves at more risk.

I drive a compact bc i don't like buying gas, but I also don't like social engineering via the tax code.

Sam

As addressed elsewhere, you certainly could add a tax which would encourage people to move to larger vehicles. This would probably (according to the study) makes us a little safer.

Is that really what you're suggesting we do? I don't think so.

If we can agree that having vastly differently sized cars is a bad thing, we should (as a society) try to minimize that danger, if possible. If we have to pick one size of car to encourage, should it be large cars or small cars?

This is not social engineering, it's about making people pay for the external costs that result from their actions.

Larry

Sam: If we have to pick one size of car to encourage, should it be large cars or small cars?

For safety reasons, the answer is clear: large cars, the larger the better (since, as another commenter above noted, not all crashes are with other vehicles). Of course, for fuel economy reasons, small cars, the smaller the better. But then there's the problem of people with families that won't fit in small cars, so we're back to large cars, unless, for reasons of over-population, we want (as a society) to discourage people from having families, except that maybe over-population isn't as fashionable a worry as it used to be, and so...?

And we haven't even touched on bumper height, design, or the color of cars yet, and which shades are statistically more likely to be killers. Those tax-assessing "encouragers" sure have their hands full. Maybe we as a society should just decree that one size (and color, design, etc.) should fit all, and have done.

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rob

I liked this paper better when Newton wrote it. Of course a vehicle that weighs 1000 lbs more than mine will be more likely to be fatal for me. The 47% figure is meaningless, unless someone can convince everyone to drive vehicles from within a thousand pound range.

The Regular Joe

why would anyone want to drive something so heavy?
http://theregjoe.blogspot.com/2011/07/change-to-over-drive.html

Geno

Why shouldn't drivers of the little eco-boxes pay a "greater fatality vehicle tax" due to the societal cost of having to support their widows and orphans or the eco-boxes come with a warning sticker showing gruesome photos of accidents involving the eco-boxes?