Four nights a week, a hoard of cyclists takes over the narrow, cobbled streets of Oaxaca, a picturesque city in southern Mexico. Pumping music, whistles in hand and shouting pro-bicycle chants, the crowd is certainly enthusiastic about bikes.

It's exactly this kind of enthusiasm for leaving the car at home that #link:http://www.mundoceiba.org/:Mundo Ceiba#, the group behind the city night bike ride, wants to promote - for the environment's sake. Transportation is a major factor in air pollution and carbon emissions, which can cause environmental and human health issues. And cities like #link:http://www.dw.com/en/top-10-worst-cities-for-smog/g-17469135:Mexico DF are struggling with the problem#.

"The idea is to get people out on bikes to avoid using the car, be more healthy and stop air pollution," Ruben Garcia told Global Ideas from the Mundo Ceiba bike shop in Oaxaca where he's general manager.

Garcia started the "Oaxaca is more beautiful by bike" movement and the night bike ride in 2008 after visiting an urban cycling conference in Mexico. It's part of a wider urban cycling network in the country and has grown from one or two meetings a month to four a week. Around 33,600 people a year now participate in the bike ride. The 32-year-old sociologist and bike enthusiast says he's excited to see more people cycling in his city and elsewhere.

"With the movement, I've been seeing more people riding the bike in the city. It's more efficient and that's why people start to like it," says Garcia. "Before this people were a little bit more lazy and were using the car more often or with a lot of stress and having no idea how to manage the stress."

It's not hard to see how tentative cyclists might catch the bike bug on the night ride. As the stereo cranks out classics like Queen's 'I want to break free' - it seems Bicycle Race was mistakenly omitted? - and the crowd winds through the streets, singing along and shouting "up with bikes" and other slogans, people stop on the sidewalk to take pictures and wave. Bikes are social.

Garcia says the night bike ride is just the first step in introducing people to the joys of cycling around a city as well as to a more sustainable way of living.

Mundo Cuibo also rents bicycles for everyday use as well as for their tours to the nearby El Arbol del Tule - or Tree of Tule - a huge montezuma cypress estimated to be around 1600 years old. The organization itself predates the night bike ride by four years and was founded to promote citizen participation as a means of solving environmental problems and is involved in reforestation and other projects.

"Everybody has to put a little bit of effort in. Everybody needs to be helping and to start a movement," says Garcia. "It is not the government that will be doing that. It's more the people who will do it and who will make a change. My contribution is to encourage people to use their cars less."

So, looks like it's time to get on yer bike.