Comment by calmbonsai
4 days ago
I can't see how a 20 km/h difference can't not make a difference averaged over so many commuter-miles, but I'm not a city planner or traffic engineer.
4 days ago
I can't see how a 20 km/h difference can't not make a difference averaged over so many commuter-miles, but I'm not a city planner or traffic engineer.
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.
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.
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.
> 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.
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> 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.
30km/h is actually above the average travel speed you typically achieve in a big city, if you take traffic jams into account.
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.
Exactly my point.
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.