Safety
WalkBikeCT posts a great essay by Todd Litman of the Victoria Transport Policy Institute on the “safety myth” offered up as a reason why a person might not walk, ride a bike, or take transit for a short trip instead of getting in their “safer” car.
A couple of excerpts:
So I asked the audience, how many have had a family member of close friend murdered by a stranger? Only one hesitant hand was raised (it was not a really close friend). Then I asked, how many have had a family member of close friend killed in a car crash? More than half the audience raised their hand. This is statistically representative: for non-poor, middle-age people, the chance of dying in a traffic accident is an order of magnitude greater than the chance of being murdered by a stranger.
These differences are even more significant when viewed from the perspective of society rather than just a single individual, since total traffic fatality rates tend to increase in a community with more per capita motor vehicle travel, while streets and public transit systems become safer as more responsible residents walk, bicycle and ride transit. One of many benefits of shifts from driving to alternative modes is increased safety and security.
Click through to WalkBikeCT for more.

This is an excellent point, however, I would suggest that there is one variable that needs to be added to the mix. That is the distance traveled per mode of transit. Because Americans walk far fewer miles than they drive, a straight across comparison is not statistically sound.
Of course, easy driving leads people to make tons of trips that are really unnecessary, and I regularly wonder what would happen if they had to cut down.