All fifty states base their speed regulations on the Basic Speed Law. "No person shall drive a vehicle...at a speed greater than is reasonable or prudent...and in no event at a speed which endangers the safety of persons or property".
Under California law,
The maximum speed limit in an urban area is 55 mph.
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 established by State law include:
The 25 mph speed limit in 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 limited.
The above speed limits do not need to be posted to be enforced.
Speed limits between 25 and 55 mph must be established on the basis of traffic engineering surveys. These surveys include:
An analysis of roadway conditions, accident records, and a sampling of the prevailing speed of traffic.
A safe and reasonable limit is set at or below the speed at which 85% of average traffic moves.
Traffic flowing at a uniform speed improves safety through fewer accidents; i.e. Drivers are less impatient, pass less often, and tailgate less which reduces 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 traffic officers aren't asked to enforce unrealistic and arbitrary speed limits.
What can we do about speeding vehicles on my street?
Speed limits are often taken for granted until a problem arises, most people pay little attention to the theory behind them. Each year, the Traffic Engineering Division receives complaints of speeding on residential streets and/or alleys.
At the written request of a resident/property owner:
Staff will monitor the location and verify actual versus "perceived" speeds on a street.
Staff will obtain accurate indications of existing speeds by radar and road tube methods.
If a problem involving higher speeds is indicated:
The Police Department is notified of the location, direction, and time of the highest recorded period of infractions.
The Police Department will subsequently place an officer at the location to issue citations and act as a visual deterrent to those who exceed the prima facie speed limit.
Following a period of time that the Police determine is necessary to curtail the behavior of the speeding motorist;
The Police Department can also install a "speed trailer" on the street where applicable.
The speed trailer provides the motorist with a visual indication of his/her current speed and the posted speed limit.
In most cases, the added attention given to a street reminds motorists of their responsibility to adhere to the posted or prima facie speed limits.
Speed Limit Misconceptions
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 accidents and increase safety.
Most drivers drive at a speed which they consider appropriate, 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 new or revised speed limits.
Furthermore, research has found no direct relationship between speed limits and accident frequency.