If I had to think of a solution to start creating a bicycle routing system, I’d do exactly what The San Francisco County Transportation Authority has done: create smart phone apps, gather information where cyclists are riding, data mine those tracks and build route suggestions on top of that knowledge.
Bicycle routing is in my opinion far more complex than car routing. Car routing is mostly based on well known and documented rules, also known as road traffic regulations. Mix in estimated traffic figures, average speeds and fuel consumptions and you get pretty decent car directions.
For cyclists, a similar rule set exists, but it’s maybe a little more, let’s call it, elastic. Cyclists use short-cuts, turn where cars can’t, go against traffic, ride through parks and on poorly documented trails. High traffic doesn’t mean slowdown for cyclists. They ride by on the bike lane on the right side of a traffic jam at almost the same speed as without traffic. But high traffic creates a security risk some cyclists aren’t comfortable with taking and rather choose a different route.
A perfect route from A to B for speedy messengers doesn’t necessarily mean it’s also an ideal route for kids. For your daily commute you probably pick another route than for weekend rides, even though it connects the same points.
Bicycle routing criteria is manifold, sometimes psychological, hard to measure and to quantify. Researching how cyclists are going, for what purpose and under what conditions, is a very smart way to get started on that topic.
