After World War II, the nation had to rebuild which increased the number of jobs. As jobs increased, wages too increased which led to many being able to afford more expensive goods. In 1957, this led to many more cars on the streets. Infrastructure was torn down and demolished to make room for cars. New developments had huge roads for motorized traffic. Bicycling had decreased by large numbers.
In 1971, out of 3,300 lives that were lost, 400 were children under the age of 14. These extreme numbers got people on the streets protesting against cars. "Stop the Child Murder," were what posters said. The people wanted safer streets for children, pedestrians, and cyclists. The oil crisis in 1973 also helped promote cycling, and soon after these mass protests against cars had caused the city to think differently. New infrastructure was then built to accommodate these new ideas. Policies to encourage cycling were put in place to remind the people how beneficial cycling is.
This video, courtesy of 'Sustainable Cities Collective,' explains the history of cycling in the Netherlands and how issues changed policies over the years.