Crash Test Dummies – the myth of SUV safety

I have long taken a pragmatic approach too transportation. Ideally we’d like to eliminate the motor car, and the heavy carbon footprint associated with them. But in practical terms that’s not going to be easy, as it would difficult in the medium term for many people to get by without cars (i.e. for some in rural area’s a car’s virtually essential), nevermind the social implications of such a draconian policy.

The compromise I have long advocated is a combination of better (and cheaper) public transport, making motorists pay a bit more for the privileges of driving (i.e. eliminating the defacto subsidy often given by government’s to motorists). And rather than trying to completely eliminate the car, focus instead on the promotion of smaller, lighter more fuel efficient cars. Several concept cars and entries in the automotive X-Prize have achieved a fuel economy of +100 mpg using existing technology and IC engines. Using more advanced technologies and alternative fuels (hydrogen, methanol, biofuels, fuel cells, electric drive, stirling engines) even higher levels of fuel economy can be achieved, +200 mpg in the case of some X-Prize entrants (see the Li-ion or Aptera).

Figure 1, A Prototype 100 mpg car by Axon

Figure 1, A Prototype 100 mpg car by Axon

But one of the core arguments against this idea of the smaller, greener cars is the “perception” that small cars are dangerous and that you’re safer in a larger, heavier older vehicle. SUV drivers, if you inquire of them how often they go off road and is they’re monster a sensible road vehicle (or are they compensating for something very small by driving around in something very big!), they will general retort about trying to keep their kids safe in a crash. But are you’re kids safer in a SUV?

In his book “High and MightyKeith Bradsher (2002) pointed out that much of this perceived safety is actually an illusion. If anything the statistics suggest that SUV’s are 6-8% more dangerous (to their occupants) than conventional cars, nevermind the hazard the present to other road users. Europe, where the majority of us drive substantially smaller cars than those in America, has a much lower rate of road deaths than in the US, approximately 2.5 times lower in fact. Now if it were true that large SUV’s (which represent 1:4 American cars v’s 1:20 on EU roads) were actually safer, we’d expect to see the opposite trend (less traffic deaths in the US v’s the EU).

Figure 2, (Left) Mini-Cooper post-crash test and (Right) an F150 SUV post crash test, still want to buy an SUV? [Credit: IIHS, 2007]

Figure 2, (Left) Mini-Cooper post-crash test and (Right) an F150 SUV post an offset block type crash test, still want to buy an SUV? [Credit: IIHS, 2007]

Perhaps the explanation for the above might be this crash test video I happened to come across the other day of an American Ford F150, one of those preposterously large 4×4 pickup’s so popular in the states. Suffice to say if you’re squeamish I won’t click on this link and watch it. While many Americans who drive such trucks (it is apparently one of the most popular cars in the US) probably feel safe in such a chunky large vehicle, the reality is a little different….as it seems to have a tendency to crumple up like a violin in crash!

Figure 3, Renault Clio Crash Test [Credit, Euro-NCAP, 2005]

Figure 3, Renault Clio Crash Test [Credit, Euro-NCAP, 2005]

By way of comparison, consider the NCAP video for my little run around (a Renault Clio 2007), a Smart City Car (which despite its small size, actually has reasonably good safety record) and of course a Prius. And should you suspect the video for the F150 is a one off, here’s a 2008 Ford Ranger crash test.

The problem with SUV’s, particularly those sold in the US, is that they are often classified as “light trucks” which means they wriggle out of the need for a whole host of rigorous crash safety requirements placed on conventional cars. While some auto manufacturers choose to implement them anyway, particularly if they plan on selling the bulk of their SUV’s as city cars (i.e. as so called Chelsea tractors), they often have to compromise, as some of the essential features of making a car safer in a car crash are incompatible with a vehicle intended to haul heavy loads or go off road.

And it’s not just certain SUV’s that can become death traps in a crash, vans can be a problem also. Particularly “flat fronted” vans such as the VW microbus (so beloved of hippies) or Nissan Hiace. Again, intuition would say that riding high in a heavy vehicle would keep you safe, but that intuition is not borne out by those pesky laws of physics….no more than global warming denial!

I discussed cars and crash safety in a prior post. But just to summarise, counter intuitively you want a car to crumple or deform to some degree in a crash. This crumbling helps to dissipate crash energy away from the passengers. Of course, in order to keep the passengers safe the one bit of the car you don’t want to crumple is the bit where they are sitting (which is exactly what happened to the F150 above, the vehicle essentially invented a crumple zone right where the driver was sitting!). So it’s a balancing act of stiffening up one part of the car, while deliberately weakening the other (but of course if the engineers go too far the crumple zone will be too weak to absorb the impact, while on the other hand too much extra weight of all that steel makes the car heavier and harder to stop).

FEA_visualization_saab

Figure 4, FEA visualization of a SAAB crash test

Meeting this engineering compromise is always something of a black art. In recent years a computer simulation technique called “Finite Element Analysis” (one of the subjects I teach) has revolutionised crash test safety, by allowing engineers to optimise a vehicles structure to achieve this balancing act.

transport_accdient_stats_2011

Figure 5, Accident rates by transportation mode [Credit: UK Department for Transport, 2011]

Of course the best way of avoiding death in a car crash is to not getting involved in a crash in the first place (such as by not driving except where absolutely necessary!). The safety record of public transportation is an order of magnitude better than private motoring.

Smaller cars tend to more manoeuvrable, don’t possess massive blind spots (SUV drivers have a nasty habit of running over small kids and pets), and are both sharper on the brakes and have less mass to slow down in the event of a crash (I recall Jeremy Clarkson, hardly a bastion of anti-motoring sentiment, complaining about the F150 and its “bottle cap” brake pads and 2 tons of weight to stop).

Also by virtue of being higher and lest stable, SUV’s, trucks and mini-vans are more prone to roll over in an accident. One of the worst case scenarios in a crash is for the vehicle to roll over. You’re chances of being killed or suffering serious or permanent disability soar if the vehicle rolls over. While roll overs make up just 2.5% of accidents in the US, they represent 10% of all accident fatalities. And SUV occupants represent a very high proportion of these fatalities (60% of all roll over fatalities in fact), as demonstrated by this video of a Jeep Cherokee failing a moose test (repeatedly!).

Figure 6, Roll over rates for different Vehicle types in the US [Credit NHTSA http://www.sscnet.ucla.edu/ssc/labs/cameron/e134s99/mobile_suv_rollover.gif ]

Figure 6, Roll over rates for different Vehicle types in the US [Credit NHTSA]

Car v’s car

Of course the SUV driver will respond by saying that surely they if they run into another car (as opposed to a offset concrete block) one is safer in an SUV than in a small car. Is this true?

Up to a point its correct, but recent redesign of cars (to account for the SUV factor) means they are more resistant to impact by SUV’s. This video (a F150 v’s a Honda Civic) demonstrates that. Again remember we want the car bonnet to deform to some degree (to dissipate crash energy). The lack of deformation by the F150 means that the driver will have experienced much higher deceleration forces and would be more likely to suffer injuries such as whip lash, neck or spinal injuries.

Also it’s worth remembering that head on collisions” represent just 2% of accidents. Side impacts represent about 29% of all crashes (and 20% of all fatalities). SUV drivers tend to come of better here…so long as it’s them being hit by normal cars rather than another SUV mind (in which case they are no better off!). But a very high proportion of car accidents are “single vehicle” incidents with cars going off the road or impacting with things other than vehicles (such as animals, trees or brick walls!). In such situations, with the SUV unable to rely on the “attenuation” of the other car’s crumple zones, its occupants are worse off than the occupants of an ordinary car in the same scenario. And as mentioned, you’re chances of being involved in such an accident are much higher in an SUV than an ordinary car (larger mass, poorer brakes, higher centre of gravity, etc.).

Also, as noted, the engineering of cars has moved on in leaps and bounds in recent years. I mentioned in my prior post  a crash test by the UK programme “Fifth Gearbetween a Volvo 2004 estate and a small 2010 Renault Modus. The outcome, had this been an actual crash, was that the Modus driver would have hobbled away as walking wounded, while the Volvo driver would have likely needed to be cut out of the car and stood a much higher probability of suffering serious lower leg injuries (read, spending the rest of his life in a wheelchair!).

Figure 7, A 2009 Chevy v's a 1959 Bell-Air....still want to drive an old car? [Credit: IIHS, 2009]

Figure 7, A 2009 Chevy v’s a 1959 Bell-Air….still want to drive a classic car? [Credit: IIHS, 2009]

In another match up the IIHS ran a 2009 Chevy into a 1959 Bell-Air. Now most people would assume you’d be safer in the big heavy old gas guzzler. But in reality the driver of the Bell-Air would likely have been killed outright, while the driver of the more modern car would have hobbled away with a sore foot. Like I said, the laws of physics don’t respect old wives tales!

Republicans v’s reality!

I recently completed an article on my energy blog about how one of the key reasons for conservative to engage in climate denial is that accepting climate change would present a serious challenge to their ideology. The author of this movie (a rather unfortunate palaeontologists who lives in Texas) debunks a number of republican myths regarding creationism. Similarly we come across another founding myth of Republicanism, that you’re safer in a big SUV than some small “European” car.

Indeed, it’s interesting to see what the car manufacturers think of SUV drivers. As mentioned in Bradsher’s book marketing data from within the industry suggests that SUV buyers tend to be:

“…..insecure and vain…They often lack confidence in their driving skills. Above all, they are apt to be self-centered and self-absorbed, with little interest in their neighbors and communities…”

“….are very concerned with how other people see them rather than with what’s practical, and they tend to want to control or have control over the people around them….”

Unsafe at any speeds…..until Nader came along!

And who do we have to thank for the current high state of car safety? Ralph Nader!  Yes! The green party presidential candidate has done more for automobile safety than the whole of the Republican party. And he did it not by bowing down to the automobile industry, but by suing them and generally holding their feet too the fire such that they began to improve car safety.

There is no reason why similar tactics couldn’t provide us with smaller, lighter and vastly more fuel efficient cars with lower running costs. And these improvement need not necessarily impact on crash safety. Indeed improvements in electronics (notably the ability of a car to detect an impending accident and activate the brakes) is probably the next logical step in vehicle safety.

Ultimately if there’s something drivers need to accept it’s that if you have to get behind a wheel (again public transport is vastly safer), you’re arguably safer in a smaller vehicle designed both to be less prone to crashing and designed not to kill the driver in the event of a crash, than in a big chunky metal death trap.

About daryan12

Engineer, expertise: Energy, Sustainablity, Computer Aided Engineering, Renewables technology
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5 Responses to Crash Test Dummies – the myth of SUV safety

  1. Pingback: The future of cars, a review of different drivetrain options | daryanenergyblog

  2. Mark says:

    My God, you’re using old data. Take a look at any current data from the Insurance Institute. It’s very clear that larger vehicles, especially SUVs and crossovers, do better in crashes then small cars.

    • daryan12 says:

      While the situation has been improving in recent years for some SUV models, the same applies to cars in general, which have also been improving. Indeed several models of SUV’s have also been getting lighter and more fuel efficient. The key myth I’m trying to dispel is that a larger, heavier vehicle is automatically safer. Not so, while there are some SUV’s with a good safety rating, there are some that are absoulute death traps, and there are some smaller cars with very good safety ratings. And furthermore any IIHS test improvement have to be balanced against the fact the higher risk of having an accident in an SUV, notably their higher risk of roll over.

      • Mark says:

        The fact is that the death rates in cars, particularly small cars, are higher than SUVs and crossovers. Even small SUVs have a lower death rate than large cars.

        As for rollovers, electronic stability control has dramatically reduced the number of injuries and deaths in SUVs. In fact, you are now more likely to die in a car that rolls over than you are in an SUV.

        http://money.cnn.com/2011/06/09/autos/suv_rollover/index.htm

      • daryan12 says:

        I suspect the author is getting “absolute” against “proportional” statistics mixed up (i.e. he doesn’t seem to be accounting for the fact that there are 4 times more cars on US roads than SUV’s, 1:20 in the EU…indeed his stat’s suggest the opposite conclusion!). Then again what do you expect the nice man from the automotive industry to say!

        Traction control and stability control can help prevent a crash, but then again lots of cars come with this feature also. So its more representative of a general improvement of overall vehicle safety. If you actually hit that barrier tho, stability control ain’t going to change the laws of physics and stop 3 tons of high centre of gravity mass from flipping over.

        While SUV safety has been improving, often because they are being designed internally to be more and more like cars, the official line is that while some SUV’s do have a good safety record, some still need improving. And there are plenty on the roads where vehicle safety wasn’t even considered when they were designed.

        Casing point, the NHTSA is currently in a dispute with Chrysler over their Jeep Wrangler model, which they want to be recalled, but perhaps understandably Chrysler don’t want to comply.
        http://money.cnn.com/2013/06/04/autos/chrysler-recall-refusal/index.html

        The IIHS has recently conducted a new set of small overlap tests and a number of SUV’s didn’t do terribly well in these tests.
        http://money.cnn.com/2013/05/16/autos/iihs-small-suv-crash-test/index.html?iid=EL

        This mirrors what I’m hearing from academics. They would argue the problem with crash tests is that we are testing for the wrong things. Its very easy for a car maker to “swot” their car for a test, i.e. make it very good at passing the crash tests (particularly when you’ve got 3 tons of mass in an SUV to play with), but then still produce a car that performs terribly in actual accidents (particularly for an SUV where things like roll overs or skidding into things are more typical of how they crash). They suggest using crash tests more to “calibrate” computer models, upon which you could then run hundreds of different simulated crashes and get a better idea of actual crash performance of a vehicle.

        And again, just to get back on topic my point is that there is nothing intrinsically safe about an SUV just because it happens to be heavier. That’s not how the laws of physics work. You could design a safe SUV (of course that’s going to be a pretty expensive vehicle), but you can also design a safe small car, which is much more fuel efficient…and considerably cheaper!

        And of course we’ve only considered the SUV drivers so far. What about everyone else on the road? What about pedestrians or cyclists? There is a certain selfishness to driving an SUV knowing you’ll likely kill someone in an accident, just so you can feel (rightly or wrongly) a little bit safer.

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