California's basic speed law reads:
"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 basic speed law is based on the belief that most motorists are able to modify
their driving behavior properly, with a minimum of assistance from the police. There is a need to set a maximum
speed limit based upon the average motorists ability to operate a motor vehicle under a given highway design.
In California, the maximum urban speed limit for all vehicles is 65 mph. However, urban freeways and
some 4-lane roads are posted to permit a maximum of 65 mph for passenger cars only. These speed limits are
the absolute maximum limits which may not be legally exceeded under any circumstances.
All other speed limits are prima facie limits ("on the face of it") which are deemed reasonable and prudent
under normal conditions. A few prima facie limits are established by the California Vehicle Code, including
15 miles per hour (mph) in alleys, at blind intersections and at blind railroad crossings, and 25 mph in business
and residence districts. Sign posting is not required for these prima facie zones. There is also a part-time
25 mph prima facie limit in posted school zones when children are present and going to and from school.
Most prima facie speed limits are established by State and local authorities who are permitted to set speed
limits between 25 and 55 mph on the basis of an engineering and traffic survey. For these prima facie limits
sign posting is required in order to enforce the limit with electronic traffic measuring devices, such as radar
and laser speed measuring devices.
As defined in the California Vehicle Code, an engineering and traffic survey is a "survey of highway and traffic
conditions which is carried out in accord with the methods determined by the California Department of Transportation
for use by state and local authorities. " The survey shall include (but not be limited to) a consideration
of the following:
- Prevailing Speeds - Speeds are observed and recorded in an unbiased manner in order
to determine the normal pace of free flowing traffic under normal conditions.
- Collision Records - An analysis of past accident history pinpoints trouble spots and
the probable contributing factors in speeding accidents. This process is crucial in the selection of effective
countermeasures most likely to correct deficiencies and improve traffic regulations and control.
- "Visible and Invisible" Highway, Traffic and Roadside Conditions - An inventory
of existing roadside conditions, adjacent land use and pedestrian facilities identifies needed maintenance
or improvements which are helpful in warning of hidden hazards. The identified hazards may warrant a reduction
in the speed limit.
If a driver exceeds any prima facie limit and a citation is issued the driver
must prove that the vehicle was being driven in a reasonable and prudent manner for the existing conditions
at the time and place of the citation.
