The Peltzman Effect

Arai Astro GX

Over the years, many aspects of motorcycles and gear have improved, and a great deal of these have been related to safety. The question is, have all these new systems and technologies made us somewhat lazy as riders? Enter risk compensation, and potentially, the Peltzman effect.

According to the Peltzman Effect, when safety measures are implemented, people’s perception of risk decreases, and so people may feel that they can now afford to make riskier decisions.

The Decision Lab

The sheer number of improvements we riders have seen is impressive for many road bikes – not just the expensive and exotic, but low priced run of the mill bikes too – better tyres, better brakes, ABS, traction control, ride by wire, reliability, radars and more are readily available.

It’s not just the bikes either – gear such as helmets have gotten much better at protecting us during impacts and slides, visco-elastic armour protects us from similar, and materials protect us better from the elements and from slides.

Over the last 20 years I’ve personally seen a lot of these first hand.

Dr. Sam Peltzman wrote a paper in 1975 called “The Effects of Automobile Safety Regulation” (JSTOR link).

Statistically, Peltzman argued (sometimes with himself in subsequent papers), the benefits of mandated safety features (such as tyres, suspension and braking improvements) actually give fewer benefits than expected, as people will be killed and injured as they take more risks out on the road, so there’s a basic question for all of us, including me:

Over time, do we take more risks in our riding by even subconsciously thinking that all our modern safety systems will protect us, or do we simply reap the benefits of riding well, and therefore have even more of a cushion of safety than before?

Peltzman investigated this initially after changes in the law requiring seat-belts.

Upon further investigation we found that the regulation had provoked an offsetting behavioral response. When we held other factors constant, the 1966 regulations [the first set of US auto safety regulations, which required that all vehicles be fitted with seat belts and other safety devices] caused more accidents; but the accidents tended to be less harmful, so the net number of driver fatalities was unaffected.

Chicago Booth

This thinking isn’t just in the automobile space, world class skydiver Bill Booth, who holds multiple patents for designs and equipment on parachutes, has his own rule on this, known as Booth’s Second Law:

“The safer skydiving gear becomes, the more chances skydivers will take, in order to keep the fatality rate constant.”

Bill Booth’s Second Law

It’s a bit grizzly to think about in Booth’s terms there, and I can’t say how statistically accurate that is but there are some figures which say in the US at least, deaths from skydiving went from 12 per million jumps in 2000, to 6 per million jumps in 2015, to fewer than 4 per million by 2020.

That doesn’t seem to back Booth’s theory, but as a thought experiment, there’s something to it I think. It also of course doesn’t speak to the number of injuries which would have been more serious – or fatal – if it weren’t for improved safety. That would mean people were still exceeding risk.

So back to the question for all of us. Do we push harder, knowing that improved safety will just work? I would say that’s true to an extent.

Sure, I’ll push my Tracer through wet corners at speeds I wouldn’t on my Cub, because all that suspension, tyre design etc etc I know will hold up, because they’re more designed for it. But in that case I’m still not really increasing my risk factor, because I’m still well within safety, right?

Thanks to this Tim Harford podcast which got me thinking about all this.

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