Viva la revolución: Mexico City cyclists fight for the right to ride in safety

For one morning every week, people on bikes and on foot rule 35 miles of central city streets, but it is not just about car-free Sundays - the world's fourth biggest city is also building a network of protected bike lanes

Stand on Mexico City's grand Paseo de la Reforma boulevard on a Sunday morning and you'll hear gears whirring, bells ringing and the chatter of voices as 50,000 people cycle, scoot and skate along 35 miles of closed roads. Stop and listen on any other day of the week and all you'll hear is the roar of 10 lanes of traffic.

This sprawling megacity of 21 million is home to 5.5m cars, and that number is growing despite some of the worst traffic jams in the world. Residents spend an average of three hours a day commuting, and car speeds during rush hour have fallen to around 7.5mph (12km/h). Although air quality has improved markedly since the city was named the most polluted in the world in the 1980s, walking or cycling along one of its many multi-lane highways sometimes feels as if you are sucking directly on a car exhaust.