Additionally, the researchers looked at these rattlesnakes in 19 different hibernacula (shared wintering quarters) at four regions of New York. Using microsatellite markers they tracked the dispersal patterns of these populations as they left their hibernacula, also tracking their reproductive patterns. They compared these data to the layout of roads and to natural barriers in the areas and found that the roads altered gene flow, effectively isolating these populations. These results were seen in each of the regions and were not affected by road type or age.
Clark, Rulon W., et al. (2010) Roads, Interrupted Dispersal, and Genetic Diversity in Timber Rattlesnakes. Conservation Biology: published online. (DOI: 10.1111/j.1523-1739.2009.01439.x)
p.s. Don't run over snakes with your car, its bad for the snakes and bad for the environment (not to mention its just plain mean).