For an uncontrolled intersection, that is no signals, yield or stop signs, vehicles must follow the standard right of way rule per Uniform Vehicle Code (UVC)Ref. 1 §11-401 that states "When two vehicles approach or enter an intersection from different roads at the same time, the driver of the vehicle on the left shall yield to the vehicle on the right." When this standard rule is insufficient, usually for safety reasons, then the intersection needs to get controlled. The level of control installed is based on criteria known as "warrants" regulated in the UVC and Manual of Uniform Traffic Control Devices (MUTCD). All intersections in California must abide by these warrants.
What are the warrants (criteria) for a yield sign?
The yield sign is used to protect traffic on one of two intersecting streets without requiring traffic on the other street to come to a complete stop. They are used on low volume roads where right-of-way rule at an intersection of a less-important road with a main road might not be readily apparent. Another reason might be where an intersection has restricted sight distance for the prevailing vehicle speeds.
How does the City decide when and where to install stop signs?
A two-way stop is used where one of the streets at the intersection is obviously more heavily traveled. The stop sign is placed on the lesser street to protect the traffic on the more major street. They are also placed where reliance on the standard right of way rule is unduly hazardous, as indicated by high speeds, high accident records, or restricted view. Prior to applying this "warrant", less restrictive measures, such as a yield sign, should be considered.
Why do the City have four-way stops?
The City tries to avoid four-way stops because of the great disadvantage of stopping all vehicles, thereby increasing unnecessary emissions of pollutants, consumption of fuel, and added noise. However, under certain special circumstances, four-way stop control may be suitable. These circumstances include where traffic signals are warranted and urgently needed but cannot yet get installed, when five or more accidents happen at an intersection within a 12-month period, and a formula based on vehicle and pedestrian volumes and where the approach speed on one of the streets exceeds 40 mph.
How does the City decide when to install traffic signals?
While traffic signals can cost anywhere from $150k to $250k to install, depending on the intersection, cost is not usually a factor used to decide whether to make an intersection signalized. To install traffic signals for any intersection in California, the intersection must meet warrants as spelled out in the MUTCD. Vehiclular and pedestrian volume is the most common factor in most of the warrants. Other factors include speed control, accident records, proximity to a school zone, and traffic flow enhancement in progressive systems.
How do you decide what the posted speed limit should be?
Most of the posted speed limits in the City were derived from traffic studies conducted for that street. The study includes vehicle and pedestrian volumes, type of development along the roadway, such as certain types of businesses or residential, and speed surveys. Typically 85% of the traffic drives at a velocity that is less than or equal to a safe speed. So that 85th percentile speed is usually set as the speed limit, unless other factors warrant a lower speed, such as school zone, accidents and so on. Remember though the basic speed law, never drive faster than what is safe.