Here are some links to independent groups making DIY transport improvements to improve pedestrian and bicycle safety, and articles about their work. Feel free to add more in the comments.
San Francisco – SFMTrA
Building DIY Bike Lanes as a Form of Activism, John Metcalfe, The Atlantic CityLab, 23 December 2016.
San Francisco Makes a Guerrilla Bike Lane Permanent, John Metcalfe, The Atlantic CityLab, 12 October 2016.
Portland, Oregon – PDX Transformation
Demanding More from the City, by PDX Transformation, The Portland Mercury, 20 July 2016.
New York – Transformation Department
An Anonymous Group Is Fixing Bike Lanes Where New York Isn’t, Sarah Goodyear, The Atlantic CityLab, 30 October 2015.
Boston – Flowers & Such: Boston Bike Lanes
A crowdfunding project raising money for flowers and safety improvements in Boston.