Hacker News Reader

Comment by uxp8u61q | Hacker News Reader

15 km/h is not "a little bit faster", WTF.

Agreed 15ks is a lot. Time to slow down before you kill someone GP.

Depends on the speed limit really. In a 90 zone it's a poor habit but common throughout Europe. In a 30, it's in the goodbye driving license territory over here.

I live in western Europe. Doing 105 in a 90 zone is not a common habit. When I'm going 90 in a 90, very few people go faster than me, and when they pass me, usually everyone in the car goes "holy shit look at these maniacs".

And energy is quadratic with respect to velocity. Going 90->105 is worse than 30->45. The only difference is that a 30 zone is usually a densely populated area, so the risks are different.

Which country? That does not match my view of any Western European country I've lived or driven in.

I live in Norway. The most common highway speed is 80, but when you see someone driving sharp 80 it's most often a novice or the car is on automatic cruise. Most people lay on 5-8 km/h but on a multi lane road people doing 90+ are not uncommon. Traffic cameras for 80 zones are typically tuned in +12.

I'm not sure where you are, but from my driving elsewhere, it appears similar in Sweden (only the posted speeds are higher), and worse in Spain & Italy.

And energy is quadratic with respect to velocity. Going 90->105 is worse than 30->45.

Since the speed delta is the same it's far worse with 30 to 45, and regulations reflect that.

We clearly have different experience on the road.

> Since the speed delta is the same it's far worse with 30 to 45, and regulations reflect that.

If E(v) = mv²/2, then E(v+dv) = m(v+dv)²/2 = mv² + m v dv/2 + m dv²/2. As you can see, the middle term is proportional to v, the initial speed. Kinetic energy does increase more going 90->105 than 30->45.

Maybe this is too abstract, so he're a concrete example. Let's assume a vehicle weighing 1 ton (1000 kg).

* Going 30 km/h => kinetic energy is 34 kJ

* Going 45 km/h => kinetic energy is 78 kJ, so about 43 kJ more

* Going 90 km/h => kinetic energy is 312 kJ

* Going 105 km/h => kinetic energy is 425 kJ, so about 113 kJ more

It's really basic physics.

Then I think you understood that 15 over 30 represents more than a doubling of the energy versus the increase by 1/3 in the (already assuringly lethal for pedestrian) 90 case.

The A10 ring around Amsterdam has a max speed of 100 (except the west side where it's 80), but when there's no traffic jam, it's not unusual for a lot of people to go at least 110.

Reply on news.ycombinator.com