Does pricey gas make cars safer?

Does costly gas save lives?

That's a question touched on in an interesting new study published this week by the Governors Highway Safety Assn., which looked at fatalities in 44 states plus the District of Columbia. Overall, the study found that between 2007 and 2008 the total number of fatalities declined in all but four states, led by a 28.5% reduction in mortality in Massachusetts.

But by comparing the percentage change in number of fatalities to percentage change in the number of miles driven in the state — a statistic called Vehicle Miles Driven, or VMT, reported by 22 of the states in question — the study makes it possible to zero in on whether the safety gains are entirely linked to the cost of gas.

How? Because time and again, surveys (and common sense) have shown that when gas is expensive, people drive less; conversely, when gas is cheap, they eat up the miles. Since cars that aren't on the road can't kill their drivers, passengers, other drivers or pedestrians, the theory goes, pricier gas would logically spell fewer fatalities. So: Cheap gas kills. And since high gas prices took a big bite out of VMT last year, it would appear a perfect year to establish that relationship.

At least in theory. Reality would appear a bit more complicated....

Here's what the study found: in 17 of the 22 states reporting fatality and VMT statistics, fatalities decreased substantially more than the decline in miles driven. In Illinois, for example, the number of miles driven decreased by 4%, year over year, but the fatality rate decreased by 16% — four times the rate expected under the pricey petrol postulate. On average, fatalities decreased at more than three times the rate that miles traveled declined.

The big outliers were Wyoming and New Hampshire, where VMT decreased, but fatalities increased. Also of interest were the roads of Vermont, which was the only state with a VMT increase (a 1% uptick), yet 10.6% more people died there than in 2007. 

What is the takeaway from all this? We're not statisticians here at Up To Speed — in fact we barely passed trigonometry and got a C- in calculus — but it would seem to indicate one of three things:

• That there is either a nonlinear, but real, relationship between miles driven and fatality rates. That seems complicated by the fact that states with the largest delta in VMT had fatality declines that were relatively smaller than those with smaller changes in VMT (for example, South Carolina had a 5% dip in VMT and a 15% reduction in fatalities, a 1:3 ratio; in Minnesota, VMT went down only 2%, but fatalities decreased 12%, a 1:6 ratio).
• That fatalities and miles driven are independent of one another. On the face of it, this seems unlikely because there is clearly a relationship to total amount of driving and vehicle-inflicted death. If nobody drives, nobody dies in car wrecks.
• That there is some relationship between the amount of driving done and the total carnage inflicted, but there are other factors out there — independent variables, so to speak — that can raise or lower the death rate regardless of changes in miles driven, such as better safety equipment.

This last one, according to our way of thinking, and the Governors Highway Safety Assn., would seem the most likely. The association's executive director, Barbara Harsha, points a finger at increased seat-belt use and increased enforcement of seat-belt laws as relevant variables.

Another spice in the soup: slower driving speeds. High gas prices may not just cause people to drive less, but more slowly. In Oregon, the average speed was down more than 1 mph last year (who knows how they calculated that). And there's little doubt that slower speeds lead to fewer deaths.

Nowhere was mentioned improved safety systems in automobiles. Can't side-curtain airbags get a little bit of glory?

—Ken Bensinger

Photo of a crash-test dummy by athena1970 via Flickr

Comments

[fcsanders]

The primary problem with higher gas prices is that when people drive less the State receives less money from the taxes on gasoline.This in turn leads the States to raise taxes in other areas of public consumption.The less we use the more taxes we will pay.It really is no more than jumping from the frying pan into the fire.....nothing changes for the consumer.

[Frankenbike]

Some of the possible independent variables:
Fewer miles driven, fewer cars on the road means clearer roads and the potential to drive faster than when there are more cars on the road.

In cases where a family has two vehicles and one is a gas guzzling SUV, the family might opt to have the more economical vehicle traveling the longer distance. Smaller lighter car not only means better economy, but better safety overall for the *other* vehicle in the collision.

If people were leaving the big SUVs at home, visibility maybe have been increased for non-SUV drivers at intersections (they don't have to pull into intersecting traffic as far to see around parked SUVs), and drivers might be able to see upcoming driving condition changes sooner because their view isn't as obstructed.

States where the income is lower may have more drivers with older cars and light trucks and dissimilar levels of safety equipment as a result. Slight reduction of collision velocities can have a profound effect on non-airbag equipped cars.

Reduced fatal accidents to decreased miles driven may be non-linear, because fewer cars on the road might mean they're more spaced out, which reduces proximity and increases the time allowable to avoid an accident. Increasing the distance between vehilces likely has an effect on every type of accident, including cars at unregulated intersections whose drivers try to cross through the gaps in perpendicular traffic. If the gaps are larger and more frequent, the risks are probably dramatically lower.

In other words, many accidents might happen not because the drivers didn't try to take evasive action, but because the drivers trying to take evasive action didn't have enough time to complete their evasive maneuvers. There's no statistical collection method current in place that measures how much more time or distance a driver would have required to avoid the accident completely.

So what we may see in these stats, is that maybe in the case of many fatal accidents, only a small increase in time or space would be needed to avoid a significant number of accidents.

The problem is, putting that knowledge into policy may lead to exactly the wrong type of decision on addressing it. For example, lower speed limits often compresses traffic to drive with closer proximity. Or leads to recommendations which are patently stupid and unenforceable.

A good example of this would be the 3 second rule. That cars should space themselves to be 3 seconds at any given speed from the car in front of them. Can you imagine any one in any urban environment in the country allowing a 285 foot following distance at 65 miles per hour? Even if the rule were only two seconds, that would still be 190 feet, and that's not going to happen either.

But reduce the number of cars on the road, and larger following distances become the norm. There's no permanent way to make that happen. Public transportation would only address that if it were fast and hugely more diversified than will ever be likely in a civilization that is now largely suburb to suburb commutes with people working all hours of the day.

Increased price of parking as well as higher gas prices only works in the short term. In the long term, increased parking prices drive companies to the suburbs, and higher gas prices get people buying more economical cars. When enough people have done that there will be the same number or more cars on the road.