This week, help shape a safer Polk Street, celebrate the 20th anniversary of Critical Mass, and more.

Here are all the highlights from the Streetsblog calendar:

• Tuesday: Shaping SF Bike Tour: Transit History. Join Shaping San Francisco co-director Chris Carlsson for this “social, historical and critical tour through the city’s transportation past and present,” exploring the remnants of abandoned networks and the turmoil that shaped transit in SF. 1:30 p.m.
• Wednesday: Polk Street Improvement Project Community Meeting. Help shape the vision for a friendlier Polk Street for walking, biking, and transit by attending the first of several SFMTA community meetings. 6:30 p.m.
• Friday: Critical Mass 20th Anniversary. Join visitors from around the world to celebrate the 20th year of Critical Mass in the city where it all started. Also be sure to check out events throughout the week leading up to the big ride. 5:30 p.m.
• Saturday: SFBC: Family Day Celebration. Just in time for Walk and Roll to School Day, this free event is your chance to connect with other biking families to share tips, play games, and have a picnic in Golden Gate Park. 10 a.m.
• Next Monday: BART Bicycle Advisory Task Force Meeting. The agenda includes an update on the Bikes-on-Board Rush Hour Pilot, discussion on the merits of a designated bike car, and accessibility recommendations for BART’s “Fleet of the Future”car redesign. 6 p.m.

Keep an eye on the calendar for updated listings. Got an event we should know about? Drop us a line.