The most cited reason that I hear from folks for not riding their bike to work is that it is too dangerous. I do agree that riding your bike, especially in America, is dangerous, but is it more dangerous than driving? Unfortunately, there isn’t a current fact based answer to this question (data is too old, or inaccurate). There is some information here, and a TON of information here. This site has a great article. It brings up a point that I feel is quite true, there are bad drivers and there are bad cyclists. No matter your mode of transport, if we could just separate the bad ones from the good ones, we would all be safer. A great deal of car / bicycle accidents are caused by stupidity from either party or both.
This site has step by step instructions for note getting hit by cars. Essentially, follow the rules of the road and pay attention! There is a good scientific study that took place in Copenhagen, Denmark over 14.5 years. It found that cycling to work (an average of 3 hours cycling per week) decreased risk of mortality by about 39% compared to a sedentary control group. This study involved 30,000 people. The study took into account age, health status, and socio-economic factors such as education. It also found that older people gained even more from physical activity than younger people.(Source: Anderson, Lars Bo “All-Cause Mortality Associated With Physical Activity During Leisure Time, Work, Sports and Cycling to Work” Archives of Internal Medicine Vol 160 No. 11 June 12, 2000.)
I think it is important to note however, that cycling is inherently safer in Denmark than it is in America. “U.S. cyclists are two times more likely to be killed than German cyclists and three times more than Dutch cyclists, whether compared per-trip or per-distance traveled. American pedestrians are roughly 3 times more likely to get killed than German pedestrians and over 6 times more likely than Dutch pedestrians.” (”Promoting Safe Walking and Cycling to Improve Public Health: Lessons From The Netherlands and Germany” September 2003, Vol 93, No. 9 | American Journal of Public Health) So, we can not exactly transfer the figures from the Dutch study, but the 39% margin does not decrease to zero, or any number close to zero.
One source of danger that I have feared is breathing in all the emissions from cars. There is a very scientific study (that has been misrepresented on some sites) that compares pollutant exposure to cyclists vs. pollutant exposure to motorists. The study found, quite convincingly, that motorists are subject to higher pollution levels. The part that bicycle promoting sites leave out is that, “calibrated for the higher ventilation of cyclists, their uptake of CO, benzene, toluene and xylene sometimes approached that of car drivers…” In addition, “The uptake of NO2 of cyclists was clearly higher than that of car drivers.” (Source: J. van Wijnen, A. Verhoeff, H. Jans, M. van Bruggen, 1995, “The exposure of cyclists, car drivers and pedestrians to traffic-related air pollutants”, International Archives of Occupational and Environmental Health, 67(3), pp.187-193.) An important point to note is the phrase, “sometimes approaches.” So - except for NO2, cyclists are NOT in-taking more pollution than drivers, though if you are operating at a highly aerobic rate, you could be coming close.
I wish that I could say that cycling in American is X % more or less dangerous than driving, but I can’t. I can say that a world in which driving (significantly contributing to negative environmental change) is the only option, is not a world I want to live in. I’m willing to take the chance of getting in an accident - and I’ve been taking that chance most days for 10 years.