Large Vehicles – Worth the Weight?

Bigger is not necessarily better when it comes to keeping people safe on our roads. 

Joe Corbett-Davies, Transportation Planner at Abley ponders the perils of the New Zealand public’s love affair with SUVs and Utes.

Our transport system is complicated. As users of this system, every day we consider hundreds of factors to figure out what works best for us given our unique situations and preferences.

For example, people buying larger or heavier vehicles trade off higher purchase and operating costs with space, comfort, and safety. Even if heavier vehicles seem safer, they are more dangerous for other road users because of their higher mass in crashes. This asymmetry can lead to an “arms race” where drivers opt for heavier and larger vehicles in response to an increase in other large vehicles on the road. The losers in this race are those driving smaller (typically also older and cheaper) vehicles or those outside of a vehicle altogether. Even drivers of larger vehicles face a cost, as they have to spend more to buy and run them.

How much more dangerous are heavier vehicles? A 2011 analysis of multi-vehicle crashes in the United States suggests that an additional 500 kg of mass in the striking vehicle is associated with around a 50% increase in the risk of a fatality in the other vehicle, even after controlling other vehicle, driver and environment characteristics. If the striking vehicle is a “light truck” (what we would call a large ute in New Zealand), that is associated with a further 40% increase in fatalities, over and above the increased harm due to the higher weight of utility vehicles.

Road crashes in New Zealand cause considerable costs to society. The Ministry of Transport estimates the total cost at around $5 billion per year, and this is likely to increase as a result of new research into the value of reductions in deaths and serious injuries. Converting estimates from the U.S. research into the New Zealand context¹, someone choosing a new Ford Ranger (2242 kg²) over a Toyota Corolla wagon (1300 kg) inflicts external crash costs of over $950 per year on those in other vehicles. Over ten years, this is equivalent to one fatality and nine serious injuries for every 2,000 additional Ranger-sized vehicles. For context, $950 is about the same as road user charges for a diesel ute driven the average number of kilometres per year.

Ford Ranger T6
Tesla Model X P100D

Electric vehicles don’t fare so well either, as a result of their higher weight. Choosing a Tesla Model X SUV (2459 kg) over the Corolla produces an estimated $900 in external crash costs per year. 

All of these costs would be higher after accounting for the increased risk to cyclists and pedestrians from large vehicles. The actual cost is even higher still, because it is unlikely that safety benefits to those driving larger vehicles outweigh the costs they impose on others. Australasian evidence suggests that, compared to the average small car, an average ute is over 50% more likely to injure those outside the vehicle, but is only 20% safer for its occupants. This means that not only is the vehicle size arms race shifting the burden of death and serious injury onto vulnerable road users and those driving smaller cars, it is also increasing the overall burden.

In New Zealand we have seen a 300 kg increase in the average weight of vehicles in our fleet over the past 20 years – roughly the weight difference between a new Toyota Hilux and Ford Ranger. This trend is expected to continue as more large and electric vehicles are added to the fleet, and older, smaller vehicles are retired. But it’s not hard to see how the cars we buy would change if drivers were required to pay for – or if the government regulated – the wider safety impacts of their vehicle choices.

1 These numbers include corrections for the much safer roads in New Zealand compared to the United States, and the reduction in baseline crash risk in the years since the U.S. study.

2 The newly-announced plug-in hybrid Ford Ranger is likely to be even heavier.