In the 1970s and 1980s a deadly cocktail of toxic factory fumes and car pollution had turned Mexico City into the world's most contaminated city.

Hundreds of thousands of people were falling ill each month, many of them children.

In response, the Mexican authorities came up with an ambitious solution: curb the use of each of the city's two million vehicles for one day a week, one of the first times any country had tried such a bold plan.

The scheme was an immediate success, reducing pollution and cutting traffic by 20 percent each day.

It was later copied in other major cities around the world.

Ramon Ojeda Mestre, the environmentalist behind the Mexican initiative, tells Witness about overcoming fierce opposition to the plan - and how some critics even predicted it would cause riots from irate motorists.

Witness: The stories of our times told by the people who were there.