How Are Speed Limits Established?
The California Vehicle Code (CVC) provides three methods for establishing speed limits. First, the state establishes a maximum speed of 65 miles per hour unless other conditions are met to result in a lower limit, except on state highways where the state may increase the speed limit to 70 miles per hour.
Second, certain speed limits are automatically set based on conditions defined in the CVC. These are often referred to as "prima facie" limits and do not require signs for enforcement. For example, the speed limit is automatically 25 miles per hour adjacent to a school when school children are present or in a residential district. Residential districts are typically the same as local residential streets. The prima facie speed limit is 15 miles per hour in alleys, or at intersections or railroad crossings where visibility is limited.
Third, in order to vary from maximum or prima facie speed limits and use radar to enforce the speed limit, the speed limit must be based on an "engineering and traffic survey" to establish a reasonable speed limit. State law does not allow speed limits to be set in an arbitrary manner.
How Do Surveys Identify Reasonable Speed Limits?
Speed surveys include information on roadway conditions and adjacent land features. The traffic incidents (collisions) are examined for typically a two-year period and compared with incident rates for similar roadways.
A key component to the surveys is the prevailing speed of traffic. The majority of drivers behave in a safe and reasonable manner. Based on actual measured speeds, those drivers who travel at excessively slow or fast speeds can be identified. The speeds of the reasonable drivers can also be determined. In a sense, drivers have cast a pure vote on what they believe the reasonable speed is based on their actual behavior. Of course, any speed limit which is established will be considered either too low or too high by some drivers.
Although surveys are used to establish maximum speed limits under normal conditions, the law does not always allow vehicles to travel at the posted speed.
The law states that "no person shall drive a vehicle upon a highway at a speed greater than is reasonable or prudent having due regard for weather, visibility, the 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."
The law also states that "no person shall drive upon a highway at such a slow speed as to impede or block the normal and reasonable movement of traffic, unless the reduced speed is necessary for safe operation, because of a grade, or in compliance with the law."
Types of Speed Limits Signs
Regulatory speed limit signs impose a restriction on a particular roadway and have a black message on a white background. Warning speed limit signs supplement other warning signs (such as for a curve) and have a black message on a yellow background.
The Purpose of Speed Limits
Speed limits provide notice to drivers of the maximum speed limit on a roadway and are an enforcement tool to assist police in separating violators from the reasonable majority.
Respect for speed limits will only be achieved through establishing reasonable limits.
If posted speed limits are set unreasonably low, disrespect is created for the limits, and since they are not set in accordance with the law, they are not enforceable with radar. The state maximum speed limit would then apply. Tickets would be considered unreasonable by most drivers, and fines and insurance costs would be exaggerated. Also, the occasional driver attempting to obey the posted speed limit may decrease safety by causing additional lane changes, passing and tailgating. Traffic flowing at uniform speeds results in increased safety and fewer incidents.
Speed Zone Misconceptions
Concerned persons sometimes want speed limits lowered to improve safety. There is a widely held misconception that speed limit signs will significantly slow the speed of traffic and increase safety. Most drivers drive at a speed they consider reasonable and comfortable regardless of the posted speed limit. Studies have shown that there is no significant change in speeds following the posting of a revised speed limit. This is true whether the speed limit is increased or decreased. Safety is also not improved by establishing unreasonably low speed limits.