bus failure

I noticed a failure mode today, of bus stops before an intersection. Bus is at the stop, having exchanged passengers. Light is green. Bus cannot pull left, because of a steady flow of traffic. Bus cannot advance, because a car ahead of it wants to make a right turn, but is waiting for pedestrians to clear. Bus is stuck.

If the stop is on the far side of the intersection, the bus might still not be able to pull left for a while, but it won't have a right turn blockage.

Hmm, OTOH given widespread street parking, the bus can't advance anyway because there are parked cars ahead. For this to work better, you'd need two lanes of traffic and no parking.

Or, of course, you change your priorities, and have bulb-out bus stops so that the bus doesn't have to leave the traffic lane to change passengers. This means the bus may stop cars behind it, but hey, priorities. Bus may have 10-100 people on it, after all.

low density walkability revisited

I still like my 2019 model of how even 3000 people/km2 can be kind of walkable (and bikable) if you do it right. Short recap: supermarket needs 8-12,000 people, so imagine a 2 km x 2 km superblock, with a market right in the center (along with bus/rail intersection). Furthest walk is 2 km or 24 minutes, from the corners, which isn't great, but many people have shorter walks, especially if density is non-uniform and clumps by the center. And 2km is 10 minutes on a slow bike, so *that's* nice. I also penciled in schools and stores and such.

At 12,000 people/km2 the scaling is easy: you have the same pattern, but in a 1x1 km superblock. Now the longest walk is 12 minutes, super easy, barely an inconvenience.

But what about 6,000? I found that annoying to think about and didn't talk about it last time. Annoyingly supermarkets might need just 8000 people... but that's 1/3 more than I have in 1 km2.

But I realized, if you take the 12,000/km2 model, and then simply remove every other supermarket in a checkerboard pattern, then you have the right population ratio to support the markets, but still no one has to walk more than 12 minutes, 1 km. You've increased the *average* walk time -- a bunch of people who were in 0-3 minutes are now in 9-12 minutes -- but not the max.

Probably not coincidentally, I read somewhere that car use drops off around 10-20 units per acre; if that's gross acre, then that's 2500-5000 units per km2, or 6250-12,500 people/km2 if each unit averages a 2.5 person household.

(And if you're wondering how that compares to real cities, this older post is useful, though sometimes neighbhorhood density would be more useful. But given that cities tend to be largely residential, a US city of 1000-2000 people/km2 is obviously not going to have much walkability.)