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.


Doug

So I would expect the impact to insurance premiums to be higher liability premiums for heavier vehicles.

Doug

Some small quibbles.

Yes, SUVs are "safer for those driving them" when an accident occurs, especially with a lighter vehicle, but due to their bigger size and rollover tendencies they are not as good as small cars as AVOIDING accidents to begin with.

Someone in a smaller car may be less likely to survive an impact with a large SUV, but it is more possible for someone in a small car to maneuver and swerve around obstacles. SUVs have a tougher time with sharp curves or sudden swerves, for example, since a higher center of gravity may cause a driver to lose control of the car more easily. An SUV driver may swerve to avoid one accident only to lose control of his or her car and cause another. Yes, he or she might survive due to the heavy steel surrounding them, but the accident might not have happened in the first place had the driver been in a smaller car.

Additionally, believing that one is safer in a big car may cause SUV drivers to take bigger risks. 4WD may cause someone to go out in a blizzard when road conditions are more dangerous for everyone or drive in conditions that would otherwise cause people to slow down or even stay at home. How many times have you been driving carefully on a snowy highway when someone in a big SUV comes barreling down the road at the speed limit or above. They're probably going that fast because they think the vehicles makes them less prone to accidents.

So, in a larger sense, smaller cars are "safer for those driving them" because their drivers are less likely to get into an accident in the first place, which is ultimately how one stays safe on the road.

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tioedong

did it ever occur to you that the "taking risks" and "going out in the snow" are only valid for city folks, not for those of us who live in the rural USA? Sometimes we have to drive long miles on unsafe roads, even on dirt or gravel roads, to shop, pick the kids up at school, etc.

And yes, it's easier to crash on an unplowed unlit narrow snowcovered road in Minnesota than a well plowed wide highway in Boston.

James

Did it ever occur to you that maybe some of us know what we're talking about? I grew up in the country, and learned to drive there at a time when the only 4WD vehicles were a few Jeeps. I live in the Sierra Nevada now, and regularly drive mountain & desert roads - including dirt ones, and regularly crossing 8900 ft passes in the winter - in my Honda Insight hybrid, which is close to being the smallest, lightest car on the road. When the road's too rough for the Insight, or I need to haul hay or firewood, I use an '88 Toyota pickup, which is maybe half the size of the SUV or pickup you think is necessary for your rural life.

Fact is, you've been fed a bunch of lies by the US automakers, who'd rather slap a box on a truck chassis than meet passenger car standards, and have become so brainwashed that you have no idea what you actually need.

caleb b

Well, maybe we should look at other factors before just adding taxes.

According to the U.S. Department of Transit, the main causes for fatal accidents are alcohol (32%), speeding (31%) especially by people 15-20 on non-interstate roads, and not wearing a seatbelt (43%)…..obviously some of these overlap.

In total, 88% of fatalities occur on non-interstate roads.

http://www-nrd.nhtsa.dot.gov/cats/listpublications.aspx?Id=A&ShowBy=DocType

Instead of a policy that taxes larger vehicle owners to pay for the damage they cause to smaller vehicle owners, why not focus efforts on reducing the factors that cause fatal accidents in the first place?

If my wife gets killed in accident involving a drunk, speeding teen driver, it’s not any great comfort to me that they paid more at the pump.

Sam

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.

By your logic we shouldn't be thinking about traffic fatalities at all since the leading cause of death is heart disease.

John Borneman

Mmmm.. while I am not necesarily doubting the statement, "By 2005 those reductions had all been gained back, and the average car was as heavy as it was in 1975", I do wonder if the median would be a better number. I wonder if in 1975 the weight of the average car was due to iron engines, thicker steel bodies, etc. Today, I suspect the average is higher due to more trucks being purchased (lots of heavy trucks averaged in with smaller ligher cars). Not sure it changes anything, but today's cars and trucks would be 'much' heavier if built with 1975 technology.

RogerP

The trouble is that the worst and least considerate drivers seem to buy SUVs. I have the impression that SUV drivers cause more fatal accidents than average

Skip Montanaro

Why are light trucks more dangerous than other vehicles? Does it have something to do with bumper height?

larry b

What a silly and misleading finding. The majority of accidents are single car, where heavier is better. Why not show the affects of weight on survival rates for all accidents?

kevin

Forget about the gas tax. It doesn't directly correlate to the weight of the car. Simply tax on the size of a car. This solves more problems than just the fatalities. It could impact congestion, parking expenses, etc.

Tax big cars. Tax them significantly.

Nick

The weight gain since the 80s is due to safety equipment and luxury features. Just look at the weight of a current BMW 3 and 1 series vs an 80s 3 series.

James

"How many times have you been driving carefully on a snowy highway when someone in a big SUV comes barreling down the road at the speed limit or above."

It's much more exciting when you round a hairpin bend on a snowy mountain road to see the big SUV bearing down on you - sideways. Been there, done that, got the seat cleaned afterwards :-)

tioedong

their conclusion: I should volunteer to pack my family into a tiny light weight car instead of buying a comfortable 4wd minivan or SUV that will fit all of us comfortably and keep us safe.

altogether now:

http://youtu.be/MqTKZgEW8pM

John B

This will drive you even crazier. The government is NOT adding an extra tax for behemoths.

At the same time the feds tell us they are raising mileage standards for cars, the giant SUV's and trucks which kill, maim and waste gasoline have been given a special TAX break this year! (The current Pres. signed this into law. Thanks.)

The tax break applies to SUV's and pickups that weigh AT LEAST 6000 pounds. Any "business" that buys one gets to depreciate it all at once instead of over 5 years for cars. A huge tax benefit that encourages them to buy the biggest and baddest vehicles.

So if that 6000+ pound vehicle tailgating you gets you upset, just remember you are paying for his right to tailgate by giving him a tax break. "Tax breaks" are paid for by other taxpayers--including those who are trying to do the right things by buying reasonably sized, good mileage cars.

Fred

the modern prisoner's dilemma

Larry

SUVs, of course, are the demon-vehicles of the eco-set, but forget them just for a minute. As I read the post, it's mostly talking about relative vehicle weights, which apply as much to the difference between full-size and compact, or compact and sub-compact, or sub-compact and micro, or micro and motor-cycle for that matter. In all crashes involving vehicles of discrepant size, the safer one to be in is the larger, the less safe is the smaller, as has long been obvious. If we're only looking at discrepant-size crashes, in other words, it's not just the hated SUVs that are the problem, it's anything heavier than a motor-cycle, or maybe a bicycle. If, on the other hand, we're really interested in relative vehicle safety, then nothing that I can see in this study refutes the case that the heavier the safer. You want regulation for safety, then never mind "light trucks" -- policy-makers should be "nudging" us all into big trucks.

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