"Safety in numbers" is the name given to the concept that getting large numbers of cyclists onto the road systems improves safety not only for cyclists, but for all road users, including drivers. This effect has been observed not only in Europe but in cities suhc as New York where traffic injuries and fatalities have gone down in parts of town that have received advanced cycling infrastructure.
In fact, cities with high usage of bicycles for transportation, such as Davis, see lower absolute as well as per-capita traffic injuries and deaths than do cities of comparable size with low cycling mode share.
Read the synopsis at Planetizen: Beyond Safety in Numbers: Why Bike Friendly Cities are Safer. The article includes a link to the formal report, entitled Evidence on Why Bike-FriendlyCities Are Safer for All RoadUsers.
The study explores how "safety in numbers" operates, and how to bring it about as well. Definitely required reading for anyone interested in cities, cycling, transport, or sustainability.