The relationship between the speed limit posted on a road, the speed the road was designed to bear and the traffic accidents that occur on the road would surprise most people. The issue of speed is contentious, but important. The National Highway Traffic Safety Administration claims that roughly one-third of all accidents are speed related. While that does not mean that those accidents are all caused by drivers who are going too fast, it does mean that rate of speed is a vital factor in many deadly crashes.
The majority of speed limits are set based on how fast traffic flows on a particular road when unimpeded. The limit is set so that 85 percent of drivers are at or below the limit and 15 percent are above. Basically, speed limits are set at a level that most people feel is a safe speed to drive. Some studies have shown that people set their speeds based more on a feeling of safety than on the posted limit. When a speed limit is changed from 55 to 65 mph, the average speed of traffic remains the same.
Roads are designed with a very different speed in mind. Design speeds are generally used to set the minimum safe travel speed on a road. Actual traffic tends to far outpace the speed a road was designed to support.
In most American cities, the car is king. Speed limits are set only with cars in mind. Bikers and pedestrians are expected to conform to the needs of drivers, despite laws stating that pedestrians have the right of way. The result is an unacceptable number of deaths from traffic accidents. Thousands die, including many bikers and walkers, to fuel our obsession with cars. It remains to be seen how long that situation will be tolerated.
Source: FiveThirtyEight, “Why The Rules Of The Road Aren’t Enough To Prevent People From Dying,” by Anna Maria Barry-Jester, 15 January 2015