Tired of waiting for the local government to build more bike lanes, a group of cyclists in Mexico City, the largest city in North America, took matters into their own hands: they painted the lanes themselves.. As traffic and pollution continue to choke cities, bicycles can ease the pain. Yet cities around the world struggle to build biking infrastructure. Grassroots activism is finding creative ways to get the job done. For more information on this episode, visit nationalgeographic.com/overheard.  Want more?  Learn why some cities in the U.S. have made huge strides in becoming more bike-friendly, while others are lagging behind. Follow our vigilante superhero Jorge Cáñez on Twitter @peatonito.  And learn more about Areli Carréon’s group—the first bike lobby group in Mexico City—at bicitekas.org.  John Pucher’s book Cycling for Sustainable Cities features a collection of research reports sourced from transportation experts all around the world.  And for paid subscribers:  Dive even deeper into the world of green transportation by checking out the September issue of the magazine, which features stories about electric cars and hydrogen-powered planes.  If you like what you hear and want to support more content like this, please consider a National Geographic subscription. Go to natgeo.com/exploremore to subscribe today. Learn more about your ad choices. Visit megaphone.fm/adchoices