If you’ve not already seen this, read it:
After being asked by officials in Pasadena, Calif., if their city “was a dangerous place to bicycle,” Jacobsen began looking at crash data from various communities where bicycle ridership had fluctuated over time.
What he found surprised him: The number of crashes involving bikes correlated with the number of riders in a community. As ridership fluctuated, so did the crash rate. More riders, fewer crashes; fewer riders, more crashes.
This happened too abruptly, Jacobsen decided, to be caused by slow-moving factors like infrastructure development and cultural change. Bicycling becomes safer when the number of riders increases, he concluded, at least in part because the number of riders increases.
The more cyclists on the road, the safer we are. Read the whole thing.