From a New York Times online article:
Copenhagen’s legendary bicycle setup has been propelled by all of these aspirations, but the critical element is the simplest: People here eagerly use their bicycles — in any weather, carrying the young, the infirm, the elderly and the dead — because it is typically the easiest way to get around.
Copenhagen’s status as a global exemplar of bicycle culture owes to the accommodating flatness of the terrain and the lack of a Danish auto industry, which might have hijacked the policy levers. Trouble also played a role.
Nearly half of all journeys to school and work in Copenhagen take place on bicycles. And people like it that way.
The global oil shock of the 1970s lifted the price of gasoline, making driving exorbitantly costly. A dismal economy in the 1980s brought the city to the brink of bankruptcy, depriving it of finance to build roads, and making bicycle lanes an appealingly thrifty alternative.