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An 2013 Washington City Paper cover story proclaimed that “there is no war on cars.” But as four-wheeled vehicles share an increasing portion of roadspace with two-wheelers, tensions are bound to arise. Cyclists get frustrated when cars block bike lanes; drivers are bothered by cyclists who slip ahead of cars stopped at red lights. While simple courtesy might solve some of these issues, other countries have better ideas. The new documentary Bikes vs Cars, which kicks off this year’s Environmental Film Festival, examines the relationship between the two entities in cities around the world. From Copenhagen, where 40 percent of residents travel to their jobs by bike, to Sao Paolo, where activists fight for safer bike lanes, director Fredrik Gertten shows what could happen if more people picked hand brakes over motors. A greener, fitter world is only a few pedals away. The film shows at 7 p.m. at the Carnegie Institute for Science, 1530 P St. NW. $25. dcenvironmentalfilmfest.org.