Speaking objectively, average motor vehicle speeds on urban streets tend to be much lower than speeds on rural roads. This provides more time to be seen, and more time for reacting/braking, as well as less severe collisions when they occur. Those urban streets where traffic does move much faster than bicyclists are more likely to have additional pavement width for drivers to be able to pass safely with less delay and without moving into the oncoming lane compared to rural roads.
But subjectively, it seems to me that urban drivers on average are more competent at dealing with traffic, and it seems there are more rural drivers who are reckless lead-foots and hesitant to brake. The frequent overdriving of one's sight distance that I witness in rural areas would result in a car-car crash pretty quickly in the city.
A bill for a graduated licensing program for teenage drivers that was introduced in our legislature a couple of years ago was staunchly opposed by a legislator from a rural area, who suggested that it be limited to urban drivers. The bill supporters subsequently did some research (with NCDOT's help I believe) and determined that by far the highest rates of serious car collisions among teen drivers happened in rural areas. The bill ultimately passed.