Cycling is at a tipping point: while some cities build bike lanes and ban cars, others are experiencing a backlash. Will the future of cities be two-wheeled? In the battle against air pollution and gridlock caused by cars, cities around the world are increasingly turning to a low-tech, two-wheeled solution. Urban cycling, however, appears to be at a tipping point. While London and even Los Angeles look to build better bike lanes, and Oslo or Madrid make efforts to ban cars from their centres entirely, other cities appear to be back-pedalling, embracing driverless cars or banning some people from using bikes altogether. On the eve of this battle, join Guardian Cities all week long as we report from the painted lines. Our correspondents have been everywhere from Tehran, where some women are defying the religious leaders who consider cycling a threat to morality, to Seattle, where bicycles have been embraced by an unlikely group: riot police.

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