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SUV owners often cite their increased height over cars and minivans as a safety feature. Yet ironically it is this very issue that lies at the heart of most SUV safety problems, for both SUV occupants and other road users.

Rollover fatalities
In the USA over 60% of SUV occupant fatalities occur in rollovers, compared with 22% for passenger cars [1]. Instability is caused by high centers of gravity, resulting from the high ground clearances needed for off road applications. Vehicles sold in the US are rated for rollovers by the NHTSA.

The rollover problem has lead to large SUVs on average providing occupant protection no better than family sedans, and worse than minivans [2,3], despite the ridiculous size and weight advantage in multi vehicle collisions.

Crash incompatibility
In multiple vehicle accidents it is those in ordinary cars who pay for SUV use. In a recent Australian study it was found that in a head on collision between a SUV and a conventional passenger car, the passenger car occupants were to 12.8 times more likely to be killed than the SUV occupant [4].  The ratio for side-on collisions was so high that reliable figures couldn't be drawn from the sample size of a few hundred fatal accidents.

In a comprehensive report by the NHTSA three reasons were identified for the excessive danger of SUVs to other cars. They were increased mass, increased stiffness, and increased height [5].  The increased height results in increased likelihood of the 4WD riding up over the other vehicle, and especially over any side door reinforcing [6].

The increased stiffness is claimed to be for off road driving.  It is also because many SUVs, from the really big ones right down to the Suzuki Vitara, are built on truck chassis, with body on frame construction, and two beams rather than monocoque construction used for cars.  Even the monocoque SUV frames are designed to be more rigid than conventional passenger car frames.

Low speed pedestrian collisions
While any car can kill a pedestrian at 40km/h 4WD's have a habit of killing at much lower speeds.  4WD's and light commercial vehicles accounted for approximately 30% of vehicles on Australian roads in 1998, but accounted for almost two thirds of child pedestrian fatalities [7].  This is an extraordinary fourfold increase on a per vehicle basis, many caused by parents running down their own kids in driveways. It has been suggested that this may be due to poor visibility due to objects (e.g. spare tyres) in the rear window, and increased height [8]. Data in the US, for all pedestrians is similar, with two times the deaths per accident when SUVs and 'pickups' were involved [9].

The number of pedestrians killed as a result of bull bars in Australia each year has not been accurately determined. Experimental studies suggest that the effect on pedestrians and cyclists of adding bull bars is similar to doubling the speed of the vehicle [10].  There are now soft plastic bull bars which in some cases may have some safety benefits for pedestrians, but most bullbars are still made from aluminium or steel.

Bullbars are designed for animal strikes, in vehicle to vehicle collisions they reduce the safety of both parties.  It is illegal in NZ to fit a bull bar to a passenger car unless it is approved and crash tested by the manufacturer.  From October 2003 this also applies to 4WD's.  

[1] "Overview of SUV's and Safety" CIREN, NHTSA, 6 September CR 181 (1999).
[2] "Analysis of traffic deaths by vehicle type and model", Lawrence Berkley Nat. lab Report T021, Mar. 2002. But also note that safety varies widely within all vehicle classes due to variations in technology, and some smaller cars to out perform some much larger ones.
[3] "Status report: driver death rates", IIHS vol. 20, no. 7, Aug 2000
[4] "Vehicle compatibility: Analysis of fatal crashes", Road safety report CR 181 (1999), Aust. Trans. Safety Bureau
[5] "Overview of vehicle compatibility/LTV issues", National Highway Transport Safety Authority, USA, Feb. 1998
[6] "Status report: Incompatibility of vehicles in crashes", IIHS vol. 38, April 2003
[7] Medical Journal of Australia, Vol. 173, 21 Aug 2000, pp. 192-195
[8] "Driveways and Deaths, a study of young children in Australia as a result of low-speed motor vehicle impacts", Road safety report  CR 208, Aust. Trans. Safety Bureau
[9] "Pedestrian injuries and vehicle type in Maryland 1995-1999", Accident analysis and prevention  Vol. 36, pp. 73-81, 2002
[10] "Bull bars and road trauma", Road safety report CR 200 Aust. Trans. Safety Bureau Dec. 2000

Peter Nicholson, 'The Australia' newspaper