Who is mostly to blame for bicycle accidents: car drivers or bicyclists? The Bay Citizen's Bike Accident Tracker 2.0 [baycitizen.org] gives access to 5 years worth of bicycle accident and collision data, which even includes information about the lighting and road conditions, the designated party at fault, or the type of parties involved (e.g. auto, bicyclist, etc.). The data about the 14,113 accidents was acquired through the California Highway Patrol, which maintains a standardized database of collisions for the whole state (in contrast to the San Francisco Police Department, who stripped out all sorts of interesting information about bike accidents before handing the data over to the Bay Citizen news organization).
Some insights from this data include how all but 4 fatal accidents appear to have occurred on roads without bike lanes, how one county seems much more dangerous than others, and that the vast majority of accidents were caused by men, regardless of being car drivers or bicyclists.
One more informative nugget: 52 percent accidents were to caused by bicyclists, at least according the police who wrote up the accident reports and sent them to the California Highway Patrol. Just 34 percent were the fault of car drivers.