From European Cycling Federation in a recent news article, a nicely-worded summary-

Cycling is the wonder drug of the transport world. It provides solutions to so many problems and unlike most forms of transport, it has lots of positive side effects. Think about it: people riding bicycles makes no noise, emit no air pollutants or greenhouse gases, they ease traffic congestion… the list goes on. But the real bread winner for policy makers are the health benefits. The more people cycle, the healthier they are. This means that cyclists don’t just ease congested streets, but they ease congested health systems.  Higher levels of physical activity translates into reduced morbidity (ill health) and reduced mortality of cyclists.