Speed zones are often taken for granted and until a problem arises, most people pay little attention to the theory behind them. The following information will help you understand how speed zones are established and what they can and cannot do.
When traffic problems occur, concerned citizens frequently ask why we don't lower the speed limit. There are widely held misconceptions that speed limit signs will slow the speed of traffic, reduce collisions, and increase safety. Most drivers drive at a speed that they consider to be comfortable regardless of the posted speed limit. Before and after studies have shown that there are no significant changes in average vehicle speeds following the posting of a new or revised speed limit. Furthermore, research has found no direct relationship between posted speed limits and collision frequency.
All fifty states base their speed regulations on the Basic Speed Law: "No person shall drive a vehicle upon a highway at a speed greater than is reasonable or prudent having due regard for weather, visibility, traffic on, and the surface and width of, the highway, and in no event at a speed which endangers the safety of persons or property."
Under California law, the maximum speed limit in urban areas is 55 mph on highways not more than two lanes in width and 65 mph on highways three or more lanes in width. All other speed limits are called prima facie limits, which are considered by law to be safe and prudent under normal conditions. Certain prima facie limits are established by state law and include the 25 mph speed limit in business and residential districts, 25 mph in school zones when children are present, and the 15 mph speed limit in alleys and at intersections and railroad crossings where visibility is very limited. These speed limits do not need to be posted to be enforced.
Speed limits between 25 and 55 mph are established on the basis of traffic engineering surveys. These surveys include an analysis of roadway conditions, collision records, and a sampling of the prevailing speed of traffic. A safe and reasonable limit is set at or below the speed of 85% of the drivers.
Traffic flowing at a uniform speed results in increased safety and fewer collisions. Drivers are less impatient, pass less often, and tailgate less, which reduces both head-on and rear-end collisions.
The posting of the appropriate speed limit simplifies the job of enforcement officers, since most of the traffic is voluntarily moving at the posted speed. Blatant speeders are easily spotted, safe drivers are not penalized, and patrol officers aren't asked to enforce and defend unrealistic and arbitrary speed limits.
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This City of Stockton web page last reviewed on --- 6/19/2015