In a widely referenced study Peter Jacobsen found an inverse correlation for the number of car accidents versus the number of people walking or bicycling. This correlation has been recently rebutted in a study in New York City as shown below.

On a related note of pedestrian and cyclist safety, it is worth mentioning the Paul Pilkington article on car accidents at 20 and 30 mph, which finds:

The chance of a pedestrian being seriously injured or killed if struck by a car is 45% if the car is travelling at 30 mph but only 5% at 20 mph. Government research showed that 20 mph zones reduced the incidence of traffic accidents by 60% and cut child pedestrian and child cyclist accidents by 67%, while overall vehicle speeds fell by an average 9.3 mph (14.9 kph). There was no evidence that accidents increased on surrounding roads. Research by local councils produces similar results. For example, Havant Borough Council has imposed a 20 mph limit on 20 miles of road and has seen traffic accident casualties drop by a significant 40%.

According to Fatality Analysis Reporting System 41,059 people died due to car accidents in 2007, of which 698 were “pedalcyclists” and 4654 were pedestrians. The total sum of this research strongly supports policy and development which encourages people to walk or bike to work, the store, school, and home – such as reducing speed limits and increasing mixed use development – is in the best interest of health and safety.