There are four identified types of bicyclists.
1. The Strong and Fearless – Ride anywhere
2. Enthused and Confident – Will handle most urban situations
3. Interested but Concerned – Probably not riding on the road often
4. No Way No How – Will never ride on the street.
Group 3, the Interested but Concerned, is byfar the largest group of cyclists. Studies have shown that these people will get out and ride their bicycles around town if they feel safe. Proper bicycle facilities make people feel safe. After riding for a while, many in Group 3 will move to Group 2.
Linked below is a fascinating article discussing this research.