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June 4, 2025

Insurance and the deadly effect of speed

We learn how to make insurance decisions and we get our yearly safe driving tip, where we look at the mathematical shape of the number of deadly accidents as a function of increased road speed.

Hello! I hope your week is going well.

New articles

When Is Insurance Worth It?

This article exposes some of the mathematical foundations on which individual insurance decisions should be made. Here's how you can decide whether or not it makes sense to get insurance, without relying on vibes or loose heuristics. Web-based calculator included!

I submitted a preview of this article to LessWrong a few months ago and it got curated there, so some readers may already be familiar with it.

Full article (8–18 minute read): When Is Insurance Worth It?

Flashcard of the week

Perhaps as the start of a summer tradition, here comes my safe driving tip for this year.

In some corners of Swedish traffic safety research, there is something called "the power model" which is a simplified relationship between increased road speed and increased number of accidents.

The reason I care about this model is not that it's very accurate (I don't know how accurate it is) but that it is very illustrative of the effects of speed on accident outcome. I have three flashcards related to it:

What does the power model say about the number of mild accidents when speeds increase from v to u?

They increase by (u/v)^2.

In other words, if speeds increase by 20 %, then the number of mild accidents increase by 44 %. Let's graduate from mild accidents.

... number of serious accidents ...?

They increase by (u/v)^3.

Huh, okay. What about

... number of deadly accidents ...?

They increase by (u/v)^4.

This means the same 20 % increase in speed increase the number of mild accidents by 44 %, but the number of deadly accidents by nearly 110 %.

The important thing here is the shape traced by these consecutive answers. Yes, clearly the total number of accidents change when speeds are increased – but the big effect comes from shifting mild accidents into serious and deadly ones.

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