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"Pavement
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About Surface Treatment
Programs (Measure D and TEA-21 Funded Contracts)
Speed limits are determined on the basis of traffic and engineering surveys and are established to facilitate the orderly movement of vehicular traffic on any given roadway or on any given section thereof. Elements
considered in traffic and engineering surveys are: Speed limits are normally established at the first five-mile-per-hour increment below the 85th percentile speed (the speed at which 85 percent of the motorists are traveling @ or below on the surveyed roadway). Prima Facie Highway Speed Limits According to the California Vehicle Code section §22349, the prima facie speed limit on all highways (including four-lane or more) is 65 mph. On two-lane undivided highways the prima facie speed limit is 55 mph. Prima Facie Street Speed Limits Fifteen miles per hour limits are applicable as follows: a) When
traversing a railway grade crossing if during the last 100 feet of the
approach to the crossing the driver does not have a clear and unobstructed
view of the crossing and of any traffic on the railway for a distance
of 400 feet in both directions along the railway.
a) On
any highway other than a state highway, in any business or residence district
unless a different speed is determined by the local authorities. All other speed limits are determined by Traffic and Engineering Surveys.
Section §40802(b) provides that prima facie speeds may not be enforced by radar unless the speed limit has been justified by an engineering and traffic survey within the last five years. General Information Many people believe that installing lower speed limits will always cause motorists to slow down and will consequently reduce accidents. Past studies indicate that this is not the case. Nationwide studies conducted over several decades reveal that the speed at which motorists drive is not always influenced by the posted speed limits, but by the type of street and the current traffic conditions. California's Basic Speed Law (CVC § 22350) provides 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 that endangers the safety of persons and property. Traffic engineering studies may lead local authorities to establish other speed limits between 25 and 65 mph. Elements considered in those studies that help determine such speeds are roadway conditions, accident records, and the prevailing speed of prudent drivers. Posting unreasonably low speed limits will make some drivers ignore the signs while some others try to obey them. This may create safety concerns because of the difference between faster and slower motorists.
Properly placed and warranted signals can improve the overall flow of traffic, but they do not always prevent accidents. Very often, accidents of certain types increase after traffic signals are installed. Signals can be very effective in reducing right-angle collisions, but they could lead to increases in "rear-end" type collisions and other kinds of accidents. Some pedestrian-related accidents may occur because pedestrians get a false sense of security when crossing signal-controlled streets. According to conclusions drawn from two studies recently conducted here in California, signals may have an adverse effect when installed at sites where there were only minor problems prior to the installation of the signals. The first study included more than 1,000 new signals and the second included 24 major California cities. A related third study, called the Schoene study, warns of a possible increase in accidents whenever signals are installed at intersections where there were fewer than 10 right-angle accidents per year prior to signalization. Signals installed at collector and local street intersections may be necessary for improving access to major streets, but they can also result in more neighborhood cut-through traffic.
The following are some points Traffic engineers take into consideration when deciding whether a traffic signal should be installed. · Is the volume of vehicles entering an intersection creating dangerous confusion or congestion? · Is traffic on the busy street so heavy that drivers on the side street will try to cross in an unsafe manner? · Is there often a considerable crowd of pedestrians waiting to cross a wide, busy, and high-speed street? · Do school children clearly require a traffic signal to cross the street with safety? · Would the signal affect traffic flow adversely because of incompatibility with another near-by signal? These are just a few of the points traffic engineers take into consideration for determining when traffic signals should be installed. Before making such determination, traffic engineers first assess whether the conditions at potential traffic-signal locations meet the requirements established in nationwide standards. When
the established appropriate standards and conditions for installing a
traffic signal are met, the signal will normally operate effectively.
When those standards and conditions are not met, the signal may only cause
more problems.
Under
the right conditions, STOP signs can be very effective in improving traffic
safety. The right conditions for installing STOP signs are determined
through existing National Standards. Some factors considered in such standards
are: Most drivers are prudent and reasonable. Unnecessary and unreasonable STOP signs only generate their contempt for traffic signs and will make them likely to violate those devices. Such violations may often have tragic results. In other words, STOP signs may sometimes cause more problems than they solve. STOP signs should normally stop traffic on the street with lower traffic volume. When both streets have similarly high volumes of traffic, four-way STOP signs should be installed. A traffic volume of 500 cars per hour during a substantial portion of the day is a determining factor for installing four-way STOP signs. Installing, four-way STOP signs is usually not recommended when traffic at intersections is unbalanced. When the volume of traffic flowing on street A is considerably larger than the one flowing on street B, motorists driving on street A will tend to consider stopping at that intersection as illogical and useless and will only do "stop-and-go" or "roll-on" types of stop. This could increase the possibilities of accidents. Installing a STOP sign in only one of two intersecting streets, however, tends to encourage drivers on the other street to increase speed since they have the "right of way" and they know others have to yield to them. People often request STOP signs for street intersections in their neighborhoods hoping to force speeding motorists to slow down. However, as some nationwide studies show, STOP signs can generate a high number of intentional violations when installed as merely speedbreakers or nuisances. According
to some studies, vehicle speed is actually reduced in the immediate area
where nuisance STOP signs are installed, but vehicle speed is also increased
between stop intersections. This results from motorists making up for
the "lost" time they spent at the stop sign. In general, low-traffic-volume neighborhood street intersections regulated under the State of California Right of Way law tend to operate better without STOP signs. This law requires all motorists approaching intersections from all converging streets to slow down to reasonable speeds. The State of California "Right of Way" law as stated in Vehicle Code § 21800 (b) (1) requires that: When two vehicles enter an intersection from different highways (streets) at the same time, the driver of the vehicle on the left shall yield the right-of-way to the vehicle on his or her immediate right, except that the driver of any vehicle on a terminating ("T") highway (street) shall yield the right-of-way to any vehicle on the intersecting continuing highway (street). It may be very difficult to remove STOP signs once they are installed. Therefore, we must be sure from the outset that their installation will be beneficial to all modes of transportation.
Yellow
traffic and pedestrian warning signs are basically used to provide a safe
and orderly flow of vehicles and people in our streets. They also provide
motorists, pedestrians and cyclists with ample warning of impending conditions. Unnecessary signs produce a dangerous false sense of security in pedestrians. A clear example of this is the "Children at Play" sign. Facts indicate that this sign does not protect neighborhood youngsters as it is intended to. There is no evidence showing that these signs have helped reduce vehicle speed and pedestrian accidents in the residential areas where they have been installed. There is no need to install signs in residential areas to "warn" motorists about already-existing normal conditions. When such signs are installed, they only give children and pedestrians a false sense of security and thus fail to improve safety. Children should not be encouraged to play in the street. In fact, Federal standards reject these signs because they openly suggest that playing in the streets is acceptable. Children live on nearly every residential block. Placing those signs in one street would require placing them in every street. Otherwise, streets with no signs might imply that no children live in that area and that motorists have the right to speed there. There are signs designed specifically for schools and crosswalks that serve a clear and practical purpose. Because of the concerns they raise, "Children at play" signs are not recognized traffic control devices and are not used in most areas within California. Warning signs are effective tools only when used to alert motorists of uncommon hazards.
Last updated: July 24, 2006 |
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About
Speed Limits
About Traffic Signals
About Stop Signs 
About Warning Signs