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Comment by Cybiote | Hacker News Reader

An important observation is that the probability of death drops very rapidly with drops in speed. A rough calculation shows that at 38 mph and a near instant reaction (as a robot should) would within ~1 second of applied breaking force, allow going from a ~70% chance of death to ~5%.

A very rough calculation: v(t) = -μgt + v_0. To reach 32 kph or 20 mph, t ~= 0.82/μ, guessing a fair μ=0.8 and the chart here https://ec.europa.eu/transport/road_safety/specialist/knowle...

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For the people that practice street-math, Kinetic Energy goes as (velocity)^2. So halving the speed reduces the energy to 1/4. A third of the speed is 1/9th the energy. etc.

As you go faster, your energy goes up exponentially. This is why there are bitter fights about increasing the speed limit on roads; they become exponentially less safe (big caveats apply, naturally).

So if you are going 10% faster (38 vs 35) you have 121% the kinetic energy.

My math says it's ~1.18 times more KE.

But yes, about 1/5th more KE with just a 3 mph difference.

Except if the speed limit is 35, you need to drive 35. You can't drive 25 just to be more "defensive", that will get you a ticket.

Typically, no. There are some municipalities and areas of road where there is a minimum speed limit, but in the US, those are very rare. Granted, a law enforcement officer has wide jurisdiction to determine if you are 'safe' to drive and a low speed may become unsafe. But they are unlikely to ticket you and are more likely to try to help you out. Driving under the speed limit may be annoying, but it is nearly-universally not illegal.

> Typically, no.

Typically it will get you pulled over. Obstructing the flow of traffic is a thing.

It's actually more dangerous as it forces other cars to change lanes to get around you.

WTF? Spoken like an inveterate speeder... it's at best equally dangerous, the effect you are speaking of happens for both higher and lower speeds. At low speeds, other cars pass you. At high speeds, you pass other cars. Either way, every pass is an opportunity for failure, and the probability is higher the higher the relative speed. However, the road, barriers, trees, etc, is always going at 0 mph, so not just the relative, but also absolute speed control crash severity. Twice the speed means 4 times the kinetic energy... speed kills.

https://www.quora.com/Do-slow-drivers-cause-more-accidents-t...

What's your point exactly? The Quora poster's argument is just a rehash of the OP and also can be restated symmetricly for over speeding as for underspeeding and thus adds nothing here.

It also fails to address my point about kinetic energy, which is proportional to the square of speed!

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