What type of cars are the safest?

REAL-WORLD PERFORMANCE ACCORDING TO ACCIDENT STATISTICS: WHAT TYPE OF CARS ARE THE SAFEST?

* ¿Qué tipos de automóviles son los más seguros?

Many people might be wondering what types of vehicles are the safest. While it is difficult to determine this (because other factors such as the characteristics of our streets and our drivers have their influence) there are statistics that go beyond theory and laboratories, and can guide us.

In 1961, Dante Giacosa, the creator of the unforgettable Fiat 600, explained that while it is true that car safety, unfortunately, at the end is defeated if the vehicle falls into the hands of the bad driver, it is also true that in the meantime it could be kept standing because the machine was driven on well-designed roads and in good condition, and also, it is equally true that such safety was possible because it was born thanks to good engineering design and good construction of the car in question. (Quoted in "30 years of work" on "Report: Safety, keyword. Advances of the Fiat Group", "Top auto" magazine, number 9, year 5, Madrid, September 1993, pages 36-37). What is remarkable about Giacosa's description is that it present the three factors, vehicle, road and driver, as intertwined factors, as if a synergy were in place.

As usually each type of vehicle is designed for a specific function and each is aimed at a specific consumer profile, saying "this car is better than that", or in our case, "in this car I'll be safer than in the other" is also complicated. Thus we see that accident statistics for different types of "vehicles" actually reflect accidents for the different types of "road-vehicle-driver" combinations. Having said this, let us try to see if we can break up this combination and isolate the safest vehicle type.

We will not consider motorcycle accidents, which as we know are absolute champions in risk (triple-dangerous or even more, according to varying statistics).

MEDICAL STATISTICS

So, Clark Chapman and David Morrison report ("Nature", volume 367, page 39, 1994) that the probability that the cause of death of a certain person would be a traffic accident is 1%. That is, for every 100 people, 99 will die (in the end, death is inevitable) for other reasons and not by a traffic accident.

Small accidents happen all the time, with minimal consequences: a broken headlight, a crushed fender, etc.. Pediatrician Lauren Daly and colleagues estimated in 2006, with the help of cases registered by the insurance companies, that only 1,74% of children traveling in vehicles which crashed were injured.

They saw that if they traveled in vans the probability was 1,71%, while if they were traveling in normal cars the probability was 1,76%. However, looking further into the statistics, they discovered that if the boys or girls were restrained by seat belts, the chances of injury fell by half compared to the chances of getting hurt if they were not restrained. With special seats, injuries decreased to one-fourth.

However, if restrained by airbags the chances of boys or girls being injured increased (rather than decreased) up to 4,7 times. The truth is that children are too fragile for these systems; it is therefore recommended that they always travel in the back seat.

It was found that for every increase of 225 kg in vehicle weight the likelihood of children being injured decreased by 14%. However, the chances for a normal car improved 1,62 times more than for a truck. Finally, considering vehicles of equal weights with equivalent child seats, they saw that cars were 1,5 times safer than trucks.

The main problem with trucks seems to be rollovers: in 2,9% of the accidents trucks ended overturned, compared with 1,2% of cars. In case of rollover the odds of children being seriously injured were more than three times higher.

This is consistent with another report, published in 1998 by the U.S. National Highway Traffic Safety Administration: of all fatal accidents in cars, rollovers was involved in 15% of the cases, a proportion that was 18% for vans or trucks, 25% for pick-up trucks and in 37% of the fatalities in trucks popularly known as "SUV" rollover made an appearance. Interestingly, a non insignificant proportion of 30% of fatal accidents of pick-up trucks occurred in urban areas.

STATISTICS OF INSURANCE COMPANIES

To try to isolate the factors that depend on the type of driver, in 2007 the U.S.-based Insurance Institute for Highway Safety, related to insurance companies lobby groups, studied accidents with 202 different vehicle models manufactured between 2001 and 2004 ("Insurance Institute for Highway Safety", Status Report, Volume 42, Number 4, 19 April 2007, available at http://www.iihs.org). Considering only models with at least 20 driver deaths in that period and disregarding passengers, only cases where the driver was a woman over age 24 but under 65 were chosen, as this type of drivers are the safest (yes, you read it right: women are statistically safer drivers than men). Some results are shown in the table below, expressed in annual deaths per million units of the model in circulation (Reliability of results: 95%):

Midsize luxury cars: 33

Very large luxury cars: 34

Very large vans: 39

Large luxury cars: 41

Large sport cars: 41

Large "4x4" "SUV": 47

Midsize station-wagon cars: 51

Large "4X2" "SUV": 57

Midsize "4X4" "SUV": 59

Very large "4X2" pick-up trucks: 60

Very large 4-door cars: 61

Large vans: 66

Midsize 4-door cars: 71

Small sport cars: 71

Small "4X2" "SUV": 76

Very large "4X4" "SUV": 76

Small "4X4" "SUV": 77

Large 4-door cars: 81

Midsize "4X2" "SUV": 81

Large "4x4" pick-up trucks: 83

Small station-wagon cars: 87

Very large "4x4" pick-up trucks: 89

Small "4x4" pick-up trucks: 97

Large station-wagon cars: 99

Large "4x2" pick-up trucks: 102

Small 4-door cars: 103

Midsize 2-door cars: 103

Very small sport cars: 107

Small "4x2" pick-up trucks: 110

Midsize sport cars: 115

Small 2-door cars: 134

Very small 2-door cars: 137

Very small 4-door cars: 148

The table shows some intuitive results, such as that luxury cars tend to be safer. This could be explained because these brands spend more on the design and construction of their vehicles. Hence their higher price, but also their higher safety. On the other hand, economy cars are among the most dangerous, for similar but opposite reasons.

It also sounds intuitive that the word "large" appears more often at the top of the table than at the bottom, where the "small" ones meet and weep.

But what is not so intuitive can better be seen if we classify these numbers according to the mass of each vehicle. This makes sense, among other reasons, because cars of similar mass usually have similar retail prices. So, we have a second table, made from data also published by the Insurance Institute for Highway Safety ("Shopping for a safer car 2011"). The same units of measure for risk as in the table above are used (approximate values):

MASS: 1100 kg

Cars and minivans: 110

MASS: 1300 kg

Cars and minivans: 80

"SUV": 80

Pick-up trucks: 125

MASS: 1600 kg

Cars and minivans: 65

"SUV": 75

Pick-up trucks: 115

MASS: 2000 kg

Cars and minivans: 45

"SUV": 65

Pick-up trucks: 90

MASS: 2300 kg

"SUV": 60

Pick-up trucks: 80

Indeed, the greater the mass of the vehicle the greater its safety (less drivers killed per year per million units). This has to do with more metal and plastic being interposed between the impact and the driver, cushioning the blow and stopping the impacting object. This is what is called "passive safety", defined as anything that helps to minimize the consequences of an accident.

But the numbers clearly show that the three categories of automotive design are not the same. This means that while increasing the size of the vehicle increases safety, this improvement is not equal for all of them: pick-up trucks, "SUV"s and regular cars (along with vans with car chassis) have different efficiencies. Light pick-up trucks are the most dangerous, along with very small cars, but midsize cars are as safe as "SUV"s heavier than them. In fact, if a car has the same weight as an "SUV" it clearly outperforms the latter in safety.

This result, which defies intuition and much lore is explained by what pediatricians and traffic authorities have discovered in relation to rollovers, but it probably holds something else: as every Formula 1 driver knows, a lower vehicle is simply more maneuverable. This is what is called "active safety", or anything that helps to avoid an accident in the first place. Trucks can not compete in active safety against cars, which have lower center of gravity and the suspension, steering and brakes designed specifically for driving on tarmac. It is not necessary for the vehicle to roll over, with the simple fact that it sways excessively is enough to have a tendency to go in zig zag and great difficulty to turn or brake. Obviously all these increases the risk of having an accident.

So, Dante Giacosa was right: it is a combination of factors. Now what remains to be done is that everyone do their fair share.

Aldo Loup.

Originally published in ABC Color on 14 September 2008. Picture: A midsize 4-door car (Toyota Camry), on the left, next to a very large "4x4" "SUV" (Ford Excursion). Which of these two is safer? Believe it ot not, the midsize 4-door car. Photo credit: Stephen Foskett (original license, of the photograph only, obtained at: http://creativecommons.org/licenses/by-sa/3.0/deed.en). With permission from Stephen Foskett.