low density and biking, American edition

[mindstalk]

Revisiting yesterday's post in American units, since I mostly want to persuade Americans.

Thesis: low-density living, with single family houses and sizable yards, is compatible with low-car if not car-free living, if you go in heavily on bicycles.

Assumptions

Assumption: quarter-acre lots, with enough fine-grained mixed use that residential lots take up half the land. 625 acres/mile2 * 4 lots/acre * 1/2 residential factor * 2.5 people/lot = 3125 people/mile2, round down to 3000. Also, a grid-like layout of bike paths if not full streets.

Assumption: an average supermarket needs 8000 people, convenience store 2000, dentist 2000, pharmacy 6000, public library 20,000, hospital 60,000. Schools can be 500-3000 students. A light rail station needs 3500 people while a subway station needs 6000 (I am least confident about these two, but did find one source.)

Assumption: an average bike speed of 8 MPH. This seems pretty slow, but in line with Dutch bike speeds, and they're the best model for ordinary people (including children and elderly) biking around the day.

Analysis

A 7.5 minute ride reaches one mile, covering a grid area of 2 mile2, or 6000 people. Enough for 3 convenience stores, 3 dentists, 1 pharmacy, and possibly a subway station. Not quite enough for a supermarket. 600 elementary school students (age 6-13).

15 minutes reaches two miles, covering an area of 8 mile2, or 24,000 people. Enough for 3 supermarkets, 4 pharmacies, definitely a station, a plethora of smaller businesses. 2400 elementary students, 1200 high school students (age 14-17).

30 minutes (commute length) reaches four miles, covering 32 mile2, or 96,000 people. Enough for a large hospital. 4800 high school students, enabling either one very large school or a choice of smaller ones.

If you go with 1/8 acre lots, you can double all the population numbers, or keep the population numbers but shrink the ride time by 1.4 (sqrt(2)): 5.3 minutes, 10.6 minutes, 21.2 minutes. (The shorter ride covers half the area, which is made up for by twice the density.)

Benefits

I think the most obvious benefit would be for families. Instead of having to drive your kids to school, likely spending more time in the dropoff/pickup lines than you did actually driving there, and needing a job compatible with school schedules, wouldn't it be nice to let them transport themselves, as was traditional until a few decades ago? Even at these low densities, it's an 8 minute trip to elementary school, maybe a 15 minute one to the closest high school. Kid wants to visit friends? There's a good chance they can just bike over. Library? 15 minute ride. It frees up parental schedules and gives the kids independence.

As things are, giving a kid independence in such suburbs has been something like "buy a $6000 used car for each kid when they turn 16, or buy a much pricier new car and pass on your old car." Compare to spending $600 on a bike and accessories, at a much younger age.

Can you bike to work? Some people can, but it's certainly not guaranteed. But there's the transit option. The densities are too low for public transit with people walking to the station, but with biking, using secure lockers or folding bikes, it's doable.

Basically, biking allows you to treat the area as if it were a walkable area with 6x the density. 3000 people/mile2 with biking, acts like 18,000 people/mile2 with walking.

(What about 18,000 people/mile2 with biking? That's pretty awesome, in terms of economic access: nearly 600,000 people in 30 minutes. But I digress.)

Probably most families would not go totally car-free; household car ownership is still fairly high in Japan and the Netherlands. But many fewer would absolutely need a car; many trips could be by bike instead (saving on gas use and CO2 emissions); people who can't drive (whether by age, disability, or poverty) would still have good options for getting around, rather than being trapped at home or at the mercy of infrequent suburban buses. And all this still with quarter-acre lots.

Disability and biking

It's often assumed that bike infrastructure is only for the able-bodied. Not true! There are various bike-like options. Tricyles if you have trouble balancing. Handcycles if you can't use your legs. Electric mobility scooters if you really can't exert yourself -- these can use bike paths in the Netherlands.

So what's stopping existing suburbs from being like this? Three main things:

• Street layout. It's fine if you live in a cul-de-sac for cars, but foot/active transport needs direct routes (more or less a grid, even if it's not rigidly so) for the analysis to work. Cut-through paths, modal filtering, whatever.
• Safety. The streets need to be such that people would trust children to use them independently. It's not that hard: wide sidewalks (hardly anyone's walking here) and protected intersections, but many such places don't have any sidewalk now. At these densities it's not like there isn't room, you just have to do it.
• Zoning. It has to be legal for there to be convenience stores and pharmacies and dentists and such within a mile of everyone's home. This shouldn't be difficult, just have 'main streets' every mile. But if there are places with multiple square miles of purely residential zoning, they'll fail at this. Similarly, you need to keep modestly sized neighborhood schools, not have big schools on the edge of town on the wrong side of busy expressways.
• Also, if it's a place that gets snow, you need to be as good at plowing the sidewalks or bike paths as you are at plowing the main streets. Again, perfectly doable.

And of course currently we don't have the transit, so the chance of many car-free households is pretty slim. But you could still replace a lot of trips, and give non-drivers more independence, by making biking direct and safe.