In the hierarchy of urban commuters in Chicago, there's no one lower than the person who bikes on the sidewalk, as we've learned since Divvy unleashed a horde of TOURISTS and SUBURBANITES wielding beastly three-speeds mean sidewalks of the Loop and the Mag Mile:

In the video discussion with Trib reporter Jen Weigel, Kass expressed sympathy for the NIMBYs’ plight. “Would you want a Divvy bike station in your courtyard?” he asked. “I still can’t stand those Divvy bike people. You know why? Go outside on Michigan Avenue… Reporters going in and out of this building almost get killed. ’Cause you’ve got some little old lady from Denmark… and she’s on the sidewalk, and she’s almost smashing into the Polish pedi-bike guys.” He later referred to the pedicabbers as “Polish, Russian, whatever.”

It's not just bike-hostile columnists who look askance at sidewalk cyclists; a lot of cyclists do, too. And there's some reason for it: it's illegal, and if you're riding a Divvy, ignorance of the law isn't really an excuse, since the prohibition is literally staring up at you from between the handlebars.

For a long time I was bothered by sidewalk cyclists too, in part for less immediate reasons than my ingress and egress into Trib Tower; cyclists on the sidewalk reinforce the idea that that's where cyclists belong, which not only isn't true in Chicago but isn't particuarly good for the evolution of transit policy.

If that seems arcane, think of it this way: everytime someone rides on the sidewalk, a driver yells at a cyclist: get on the sidewalk! Sigh. And I suspect that most cyclists have been told that once or twice. Certainly lots of cyclists have irritated stories of having been told this.

But the deeper I get into transportation policy, the more sympathy I have for those drivers and the cyclists who follow their commands. Because, almost everywhere else, it's totally legal to ride on the sidewalk.

Take California. Recently Christopher Kidd, a senior planner at Alta Planning + Design—the folks who brought you Divvy in the first place—took upon himself the unpleasant task of mapping sidewalk cycling rules in Los Angeles and San Francisco, something I've been doing less systematically in Illinois (h/t to @krtierney and @jongraef for a helpful chat the other day).

Here's what the Bay Area looks like:

By contrast, in most of the Greater Los Angeles area, cycling is allowed on the sidewalks, but it's also a patchwork.

The same is true in Illinois. It's legal to ride a bike on the sidewalk throughout the state, unless prohibited by localities. Chicago prohibits it unless you're 12 or younger. DeKalb, on the other hand, prohibits cycling on the sidewalk only in the Central Business District, a common restriction. DeKalb's CBD looks like this:

It's the big red spot. Keep that mental map in mind if you bike in DeKalb.

Or, more confusingly, Evanston: "No bicycle riding on sidewalks is permitted in the central business district designated as D1, D2 and D3 districts in Evanston's zoning ordinance or in any other district where signs prohibiting sidewalk riding are posted."

In practice, zones D1-D3 make up only a tiny part of Evanston.

Get off the sidewalk, moron. Can't you tell you just passed from a D4 Downtown Transition Zone into a D2 Downtown Retail Core Zone?

Kidd spent a year looking up the sidewalk rules for all 537 cities and counties in California. A wide plurality, 41 percent, had no rules one way or another; 19 percent prohibited all cycling on the sidewalk; 22 percent permitted cycling on sidewalks outside of business districts, variously and opaquely defined; another eight percent permitted cycling on sidewalks anywhere.

Legally, it's chaos. "The sad reality of California’s approach is that no one knows what laws apply where," Kidd writes. "Crossing a city limit subjects bicyclists to entirely new rules, and there is almost never any signage alerting bicyclists to changing legal requirements. Even when sidewalk riding is banned in the business districts of contiguous cities, they may have wildly different definitions of where that law applies."

And it's a patchwork across the country as well. In Chicago it's illegal unless you're 12 or younger. In New York it's illegal unless you're 12 or younger and riding a bike with wheels less than 26" in diameter. In Houston it's illegal in business districts. In Seattle it's legal. In Austin it's legal, with twelve different exceptions. And so forth.

Commuting is inherently habitual, and a lot of people are habituated to cycling on the sidewalks. From the perspective of a small municipality, this might make sense—if you have zero bike infrastructure and low pedestrian traffic, permitting cylists to use the sidewalk is a cost-free way of preventing citizens from getting maimed. Nationwide, it creates an unpredictable patchwork of laws on streets and sidewalks that are otherwise designed (ideally) to be predictable across jurisdictions. A city full of tourists and transplants pulls in a lot of different habits onto narrow sidewalks.

So when a driver yells at you to get on the sidewalk, or a Divvy rider lumbers around a group walking three-wide on Michigan Avenue, it's worth keeping in mind that, while they're not following the local law, there's a very good chance they're just doing what they've always been told to do.