Because it's not an average speed but max speed. Higher max speed in traffic doesn't make an average speed higher because it makes the traffic less smooth.

For example in Switzerland on some highways during rush hour the speed limit goes down to 80km/h. They analyzed it and it turns out it's an optimal speed limit for throughput.

The average commute is not entirely within the streets with the 30 km/h speed limit. City planners usually try to route car traffic away from residential areas and places with large numbers of pedestrians, through arterials, freeways, and the like, which will have a higher speed limit.

Most of Amsterdam is 30 km, including through roads. But it's Amsterdam through roads, so it's mostly two lines one way, a dedicated tram track in between, trees that separate the road from a bike path and all that. Actual in-district roads where unsupervised 8 year olds are cycling to school and back are 15 km/h.

Suppose your city has a stretch of road between two traffic lights that, if you leave traffic light #1 and accelerate normally up to 40 units, will force you to stop at light #2 (lest you commit a traffic violation of running the light), whereas if you accelerate normally up to 25 units between the two lights, you will find that the second light has changed before you you reach it (i.e. giving you the right-of-way) and without your needing to slow down or stop beforehand, plus allowing you to pass those who are stopped at the light in the lane next to yours because they accelerated too quickly to to to high a speed after the first light and were made to stop due to reaching light #2 earlier than you.

30km/h is actually above the average travel speed you typically achieve in a big city, if you take traffic jams into account.

Exactly my point.

Yes, take Lake Shore Drive in Chicago. 4 or 5 lanes in each direction, 30mph speed limit, and average speed is often about 5-10mph.

You don’t need to be either.

Suppose a trip is 5km.

At 50km/h, that trip takes 6 minutes.

At 30km/h, that trip takes 10 minutes.

In practice, this naive way of calculating this doesn’t even reflect reality, because odds are the average speed of a driver through Helsinki was around 30km/h anyways. Going 50km/h between red lights doesn’t actually make your trip faster.

> In practice, this naive way of calculating this doesn’t even reflect reality, because odds are the average speed of a driver through Helsinki was around 30km/h anyways. Going 50km/h between red lights doesn’t actually make your trip faster.

This is a wonderful explanation.

Though I've lived in Europe (Düsseldorf and London), my default sense of urban density is still American so it was hard to fathom such a low potential average speed. In London, I didn't bother with a car.

> Going 50km/h between red lights doesn’t actually make your trip faster

Except when it does, due to horrible traffic engineering practices.

There were a pair of one-way streets in the downtown of my city. Both attempted to have "green wave" setups for the lights. One worked pretty well, the other was okay, but whatever.

The problem was that the road itself was signed at 30 mph, but the lights were timed at 40 mph. It literally encouraged people to speed if it were not too busy (e.g., after business hours).

I saw the reverse once. Some town in the (US) Midwest when I was a kid. Downtown had signs that said "The traffic lights are synced for 25 MPH". It wasn't a speed limit, just a statement. When you figured out that they were telling the truth, you started driving 25.

That would be sensible.

If I'm being very charitable, I would say you might naively set this up so that the next light's stopped traffic clears just before the previous light's traffic arrives, and perhaps that's how it worked during the day (I was a teen, I didn't go downtown during business hours much). After 5, it just encouraged you to punch it to make them all in one go.

I'm not an advocate for speeding in the cities, but this example is really bad - it says my trip time will be extended by 66%! For a really short one, it doesn't matter, but when you drive 40 minutes initially, it's really unacceptable for most.

> it says my trip time will be extended by 66%

Yeah 66% is a higher number, so it seems worse if you literally don't think about it at all.

Its 4 minutes. If its that important your car would have lights and sirens on it.

And it isn't a bad example, unless things are quite different in Finland, the vast majority of car trips taken in the US are under 6 miles (~10km). If you're taking a 40 minute trip on crowded, surface streets in a dense city and not going on a motorway, that's your choice, and frankly, quite selfish of you to not expect to go slow. I frankly don't care how long it takes you to get somewhere in a huge car through a city going faster means endangering other people.

Within a city it really doesn’t matter because it averages out.

I’m an avid cyclist in a US city. There’s a pretty large radius around me in which driving is <= 5 minutes quicker, not counting time to park. Plus cycling often leaves me directly by my destination. I can’t imagine how much more convenient it would be in a dense European city.

Anyways, what the hell is everyone in such a hurry for? Leave five minutes earlier. Cars are absolutely magical. Drivers sitting on mobile couches while expending minimal effort? Magical. So, ya know, adding a few minutes should really be no big deal. Which I doubt it does.

Big, open highways are different. Or at least I’d imagine them to be.