Are SUVs killers?

Railway timetables - Monty Python does Agatha Christie

My hate-hate attitude towards SUVs hasn’t improved after reading a new US research paper, The pounds that kill, by two University of California (Berkeley) researchers. They show being in a vehicle struck by a 1,000 pound heavier one results in a 47% increase in the probability of a fatality in the smaller vehicle (the paper might be gated for some – here’s an ungated version that looks very similar).

The authors note that from 1975 to 1980, the average weight of US cars dropped from 4,060 pounds to 3,228 pounds in response to higher petrol prices. However average vehicle weight began to rise as petrol prices fell in the late 1980s and by 2005 it was back to the 1975 level. In 2008 the average car was about 530 pounds heavier than it was in 1988.

A key reason for increasing weight is the safety “arms race”. Drivers seek large vehicles because they’re thought to be much safer for occupants than smaller ones, however they are more hazardous for other travellers in smaller vehicles. As the average size of the fleet rises, there’s an incentive for all drivers concerned about safety to trade-up. The authors note the “safety benefits of vehicle weight are therefore internal, while the safety costs of vehicle weight are external”.

Safety is a key public policy issue because road accidents are as dangerous to life as lung cancer. Moreover, traffic accidents kill more Americans aged under 40 years of age than any other cause. While only as quarter as many people die on roads each year as die from lung cancer, the average age of a road accident victim is 39 years compared to 71 years for lung cancer. The aggregate years of life lost from both causes is similar.

Noting that no detailed attempt has been made to measure the external costs of vehicle weight, the authors sought to:

quantify the external costs of vehicle weight using a large micro data set on police-reported crashes for a set of 8 heterogeneous states…..The data set includes both fatal and nonfatal accidents…..The rich set of vehicle, person, and accident observables in the data set allow us to minimize concerns about omitted variables bias.

They estimate a 1,000 pound increase in striking vehicle weight raises the probability of a fatality in the struck vehicle by 47%. Moreover, they find that light trucks like SUVs, pickups and minivans “raise the probability of a fatality in the struck car – in addition to the effect of their already higher vehicle weight”. The authors suggest this additional effect could be due to the stiffer chassis and higher ride height of light trucks, or possibly to the behaviour of light truck drivers.

A difference of 1,000 lbs is equivalent to 454 kg. Consider that the kerb weight of a Toyota Corolla Ascent Hatch in Australia is 1,260 kg, whereas a Toyata Landcruiser varies between 2,555 and 2,720 kg, depending on model. Consider also that a two-seater Smart ForTwo weighs around 750 kg whereas the entry level Holden Commodore Omega weighs 1690 kg.

The authors also considered whether a simple petrol tax could be an alternative to internalize most of the external costs and conclude that:

A simple gasoline tax that internalizes the fleet weight gain since 1989 is 27 cents per gallon. We further calculate that internalizing the total cost of external fatalities due to vehicle weight and operation, including crashes with motorcycles and pedestrians, requires a tax on the order of $1.08 per gallon.

Care needs to be taken in extrapolating from other countries to Australian conditions. For example, it is commonly observed that US drivers and passengers are less inclined to wear seat belts than their Australian counterparts. SUVs and pickups probably don’t make up as large a share of our fleet either. Nevertheless, were these calculations to apply in Australia, they imply a tax of around 30c per litre would be required to internalise the total cost of fatalities attributable to vehicle weight and operation.

Such a tax simply makes drivers of heavier vehicles “pay their way” in terms of the additional social costs imposed by their extra weight. It wouldn’t eliminate all fatalities although it should reduce them. If a tax is politically too hard (remembering the Howard Government eliminated indexation of the petrol excise) then there’s an argument for a second best policy of imposing higher fixed charges on heavy vehicles.

I admit to being somewhat reactionary and maybe even irrational when it comes to people who drive big vehicles when a smaller one would be adequate for the job they ask of it. I don’t mind people living in McMansions as long as they pay their external costs but I’m not as accepting of McTrucks, even if they pay their way. It would be little comfort to know that the SUV driver who injured me or mine had actually paid for the (economic) “right” to do it!


7 Comments on “Are SUVs killers?”

  1. Natronomonas says:

    On the fixed charges, it seems like TAC insurance would be a great way to capture the weight externality. I’m not sure people would notice so much at the bowser, but seeing your rego+TAC as 2 or three times the cost of a lighter car might quickly persuade you to shift to a lighter vehicle.
    Petrol taxes may well capture the difference but the pain is dispersed and consequently easier to ignore!

    Plus with weight there’s the known greater impact of heavier vehicles on roadway deterioration, so lighter vehicles reduce maintenance costs here too.

    Interestingly, the NY Times ran an article recently about fuel-efficient used cars sometimes holding or even increasing their value in response to higher ‘gas’ prices there – http://www.nytimes.com/2011/06/24/business/24auto.html

    • I think a higher petrol tax would be a good thing regardless of these findings. Cars in general are already heavily subsidised.

      This said, I agree that most users of 4WDs or equivilant massive cars should be paying more for their rego and TAC. Perhaps an exception should exist for people that can show its necessary for work, or a tax-rebate or something.

      • Natronomonas says:

        No, no exceptions. If it’s needed for work it already gets a tax break, and you can pass on increased costs to your customers. If your competitors can do without a large vehicle and consequently beat you on price it’s a business decision you made to stick with a large vehicle.

  2. TomD says:

    The raised height of SUV’s also adds to the safety and accident risk as normal sedans can no longer see over or around them to assess what the traffic is doing a few vehicles ahead. It’s the equivalent of driving behind a truck and the moving wall they represent.

    Another factor in the heightened damage and risk of death or serious injury from the giant SUV’s and pickup trucks is that their bumper bars are out of alignment with a sedan’s. An easy legislative fix here – force them to be lowered to match. Some models are already doing this apparently.

    Finally there is the heightened head lght beam which again could be lowered to NOT dazzle sedan drivers and increase accident risk as well.

  3. Q.Maisie says:

    Go Melbourne Urbanist! You’ve touched a chord with me!

  4. Chloe says:

    Wow… this makes me want to switch to an SUV. Sorry but I’m a very safe driver so I have no qualms being behind the wheel of a big car. I’ve been driving ten years without any incident and that includes traffic infringements and parking tickets, let alone traffic accidents. Personally, if someone else is going to cause an accident, I’m now thinking I’d rather be in the bigger car.

  5. Bob says:

    I don’t know about Australia, but in the US, the reason SUV’s are so popular is the nanny laws on car seats. The car seat our infant sits in barely fits in a Honda Accord. I’m only 5′ 7″ and when I push the seat back to where it needs to be for me to drive, I hit the car seat. Anyone taller would be unable to dive that car with the car seat in it. Here, the nanny state democrats have even pushed legislation through that requires children up to 90lbs to use car seats. So what are people supposed to drive who have 2 or 3 children? The irony is that the politicians pushing for nanny car seat laws are the same people pushing for smaller cars. THEY are the reason we are all forced to drive huge SUVs in the first place. What do they expect manufacturers to do? Defy physics and make small cars with huge interiors?


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