As it happens, I spent the spring of 2010 living in a city that has a 20 percent bike mode split. Aarhus, Denmark’s second-largest city, with formidable hills and about 315,000 residents (1.2 million in the greater area), has been rolling out protected bike lanes over the past few decades and continues to promote bicycling through a campaign called “8,000 Reasons to Cycle.”
Like San Francisco, Aarhus is improving its bike infrastructure to catch up with the most successful cycling cities , like nearby Copenhagen , which has a citywide bicycling rate of 37 percent (and is shooting for 50 percent by 2015 ). You can check out Aarhus’s three-year Cycling Action Plan here [PDF ].
The Aarhus campaign video  provides a nice glimpse of what the “20 percent” vision would look like: groups of cyclists, young and old, using dignified, dedicated bicycle infrastructure everywhere you go. It also lists a few of the “8,000 reasons to cycle” (in case you’re wondering, “8000” is the Aarhus postal code). Here are the translations from Danish:
- Reason #674: Big smiles
- Reason #762: Exercise and fresh air
- Reason #2,548: Faster through traffic
- Reason #6,237: Quality time with the kids
- Reason #94: CO2-neutral transport (well, that one’s in English)
All these reasons are great benefits of cycling, but what Aarhus, San Francisco, and many other cities  around the world find time and time again  is that the most important factor that gets people to bike more is safety — a convenient and seamless network of calm streets and protected cycling facilities.
San Francisco’s own progress  is already highly visible during rush hour on Market Street, the busiest bicycling street west of the Mississippi, according to the SF Bike Coalition, where bicyclists make up as much as 75 percent of roadway traffic . That number only seems to have grown since the SFMTA has added green , post-separated  bike lanes west of 8th Street and diverted car traffic  off of Market.
Who knows — it could look something like Copenhagen on Bike to Work Day  this Thursday.