A common question, but one that is rarely answered, among drivers is why the speed limit is set in the way that it is. Various suspicions work to explain the logic of speed limit values, which range from the simple assumption that lower speeds correlate with lower incidence of accidents, to conspiracy theory-esque claims that states are somehow punished by the federal government if their maximum allowed speed exceeds a certain number. The reality behind the establishment of speed limits is somewhat complicates, and takes into account research on accident rates at a given speed as well as the design of the road, the surrounding terrain, and overall driving behavior independent of the posted speed limit.
The exact combination of factors that determine speed limits varies from state to state. In Missouri, one of the most important factors is actual driving behavior. While the common assumption is that increased speeds lead to higher accident rates, and lower speeds to lower accident rates, this isn’t completely accurate. Most studies have shown that drivers tend to move at speeds that they feel comfortable and safe at on any given road and in any given driving situation. Speed limits that are set to reflect the approximate speed that most drivers feel comfortable going on a given road are thus ideal. If a speed limit is set too low, drivers tend to become frustrated. Ultimately, an improperly set speed limit leads to a situation where there are a group of drivers moving at the set speed limit, and a group of drivers frustrated with the slow moving drivers around them. This situation leads to more accidents than would be seen with a higher speed limit that reflects normal driving behavior.
Of course, road type and engineering are also factors in determining the speed limit. For a divided, straight, multi-lane highway, Missouri drivers can expect the maximum speed limit, 70 mph. Winding, undivided, or urban highways have slightly lower speed limits, usually between 55 and 65 mph. Residential street speed limits are reduced further to account for increased traffic and pedestrians, usually to between 35 and 45 mph for arterial roads, and lower for minor residential streets. Thus, if you’re ever unsure of the speed limit in an area, you can make an educated guess based on the road conditions and the speed you instinctively feel comfortable driving at, though it’s usually best to err on the side of caution and go a little slower to be sure to avoid a speeding ticket.