Safe Driving Bonus Tip

A few weeks back, I wrote this post about how to make driving as safe as flying on a commercial airline. The three basic measures are:

  1. Always wear your seatbelt.
  2. Never drive with a BAC of .02 or above – the legal limit is way higher than where any person should consider driving.
  3. Drive a heavier SUV. Heavier cars or SUVs are a bit safer and an SUV tends to be safer than a car of the same weight.

If you combine those three simple tips, driving is almost, but not quite, as safe as flying on a commercial airline. Today, I have a bonus tip. This tip is new enough that there isn’t direct evidence on how it effects mortality, but there is very strong evidence that it does cause a very large drop in accidents.

The tip is to drive a car with automatic emergency braking (AEB). AEB takes tools more famous for self-driving cars and puts them in cars you can buy today. Toyota started including AEB as an optional add-on in 2015. This paper collects collision data for Toyotas with and without AEB from model years 2015 through 2017 and compares their accident rates. Of the one million plus cars followed in the study, about 40% had the AEB upgrade. The study finds that cars with AEB were 37% less likely to be the striking car in a front-to-rear accident, exactly the type of accident AEB is meant to avoid.

The AEB upgrade wasn’t randomized, so it’s possible the people buying the AEB upgrade live in safer areas or are more cautious drivers – they are paying for a safety upgrade after all. But the authors have a useful quasi-control: they count accidents where the AEB-enabled car is struck in the back by another car, which the AEB can’t do anything about. They find no difference in that type of accident. So we don’t need to worry that this correlation is just the result of people with AEB-equipped cars driving in safer areas. That said, in a rear-end accident, the striking car is probably the at-fault driver. It’s still possible that drivers buying AEB are more cautious than other people who live around them, so they might rear-end fewer people even without AEB.

The study didn’t track fatalities and I have no idea what fraction of fatalities come from front-to-rear accidents, so I can’t guess how much a 37% reduction in that type of accident translates to fatalities. But this article (paywall) says the Insurance Institute for Highway Safety estimates the feature will prevent 28,000 crashes (per year? the quote is ambiguous) by 2025. Apparently AEB will come standard by 2022. Toyota, for its part, claims it already includes AEB on 90% of the cars it sells. Our roads will be safer when most cars are equipped with AEB.

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