There is an interesting study I happened upon on a UK blog called Bike Hub discussing a study done by researchers at Newcastle University that found
drivers who didn’t find the highways taxing enough were more prone to speeding or overtaking as they sought excitement. As a result the researchers suggest that making roads more complicated by building in more obstacles could actually make them safer.
This study certainly seems to support some of the traffic calming measures we are beginning to see in the US, like pedestrians bump outs, chicanes, and chokers. It also supports the notion that more cyclists on the roads means greater safety for cyclists. All of these cause motorists to use a greater portion of their mental capacity to operate the vehicle, which they claim ultimately results in safer drivers. Of course, here in the US, we would also need to convince the motorists to stop talking on their cell phones, quite trying to read the newspaper while driving, and generally pay more attention to the task at hand.