Lee celebrated the day devoted to bicycling by riding on a newly completed protected bike lane on Polk Street between Market and Grove streets.
The new "contraflow" lane, which takes riders against traffic on a lane painted green, was hailed by Lee and other elected officials for creating a safer passage across Market Street and into the Tenderloin neighborhood and beyond.
This year's Bike to Work Day event included 11 commuter convoys rolling in from throughout the city that were led by many district supervisors.
Supervisors Katy Tang and Eric Mar biked some of the farthest distances from the Sunset and Richmond districts, respectively.
At a news conference on the steps of City Hall, Mar called for more bike improvements in other parts of the city.
Supervisor Malia Cohen came in from the southeast neighborhoods and vowed to make the area better connected to the rest of the city for bicyclists, who often get bogged down in what is known as the "hairball," where Potrero Avenue, Cesar Chavez Street and Bayshore Boulevard intersect underneath U.S. Highway 101.
Supervisor Scott Wiener called for an end to double parking that blocks bike lanes, while Supervisor David Campos pledged to include more funding in the city budget for the multi-agency "Vision Zero," a goal to reach zero traffic fatalities by 2024.
Police Chief Greg Suhr and Fire Chief Joanne Hayes-White, who both biked to City Hall this morning, recommitted to supporting Vision Zero.
"Sadly, we are not going to make that goal this year," Suhr said, but he noted that bicycle collisions are down 16 percent so far compared to the same time last year and that there is more enforcement on the streets.
There have already been seven fatal pedestrian collisions this year following a deadly 2013 with 21 such incidents, as well as four involving bicyclists.
Hayes-White said the fire department is committed to make sure everyone is safe on the road and that her department "fully embraces Vision Zero."
San Francisco District Attorney George Gascon told the bicyclists in front of City Hall, "I look forward to the day we won't have a single traffic fatality."
Looking at the dozens of cyclists who stopped by Civic Center Plaza, Board of Supervisors president David Chiu, an avid cyclist, recalled, "In the 1990s it was lonely on the streets."
According to the San Francisco Bicycle Coalition, the organization behind today's event and rides, there are an average of 3,000 eastbound trips made on Market Street every day and bicycle ridership citywide increased 14 percent between 2011 and 2013.
Volunteers and staff from the SF Bicycle Coalition set up 26 energizer stations throughout the city this morning, offering free bags, bike information and fuel -- in the form of bagels and coffee -- for participating riders.
The stations will be back up for the evening commute starting at 5 p.m.
The mayor and several other leaders today called for the passage of two November ballot measures that include a $500 million transportation bond and a state vehicle license fee increase.
Wiener said if the measures pass, "we will have permanent sustainable funding for road resurfacing."
San Francisco Municipal Transportation Agency director Ed Reiskin said the funding would also support transit system upgrades, along with pedestrian and bike-specific efforts.
Reiskin noted other recent SFMTA projects, including improving six miles of bike lanes, adding bike parking, and enhancing projects such as the Bay Area Bike Share.
According to city officials, to keep up with demand San Francisco needs to invest $10 billion in transportation infrastructure through 2030.
More information about Bike to Work Day can be found at sfbike.org/btwd.