affic Operations

Having this two-way communication with field equipment allows traffic technicians to monitor traffic signal data and video and to make changes and improvements to traffic signals right from the office.  We are also able to collect traffic counts using the cameras and detectors connected to the City’s Traffic Operations Center.

The ability to monitor traffic signals from a central location also allows for the instant notification of equipment malfunction (loss of power, signal in flash, detector malfunction, etc) and allows staff to respond quickly to malfunctions and mitigate problems in real time.   

T

raffic Signals

Traffic signals are installed at intersections to efficiently assign the right of way to conflicting streams of traffic.  The City of Pleasanton has more then 100 traffic signals in town.  Each individual signal (and the system as a whole) is constantly analyzed to ensure maximum efficiency and safety while minimizing delay.  All of Pleasanton's traffic signals are traffic actuated.  Traffic actuated signals detect vehicles (including bicycles) and adjust the timing to optimize traffic flow at the intersection.

Some of the advantages of properly installed traffic signals include:

• Provide for the orderly movement of traffic
• Increase traffic handling capacity at intersections
• Reduce frequency of certain types of accidents
• Provide opportunity for continuous movement of traffic at a given speed along a route (signal coordination)
• Allow minor street vehicles and pedestrians to enter or cross the major street

Improperly installed traffic signals may cause:

• Excessive delay
• Disobedience of the traffic signal
• Use of alternate routes to avoid traffic signal
• Increased accident frequency
  
  ignal Timing

Traffic signals at an intersection are operated by a controller that is connected to vehicle detectors and the traffic signal lights.  We use two types of detectors: inductive loops which are buried in the ground and detect metal objects passing over them, and digital cameras which detect the change in contrast as a vehicle passes through a detection zone.  When a vehicle is detected it passes a signal to the controller.  An intersection equipped with detection is said to be actuated.

The controller is responsible for receiving the signal that a car is waiting and “servicing” that vehicle by giving it a green light.  To accomplish this, the controller is programmed with all of the different ways a car can travel through an intersection and those are combined into groups called phases (e.g., the two through movements on a major street could be two phases operating simultaneously).  The controller and a supplemental “conflict monitor” will not allow the signal to service conflicting phases at the same time (e.g., let the through traffic on the major and minor street be serviced at the same time).

The controller is programmed with how much time in seconds each phase needs for the following elements: the green interval, the yellow interval, the all-red interval, the pedestrian WALK interval, and the pedestrian crossing interval. The time it takes to complete all of the phases one time is called the cycle length.  The maximum cycle length is 120 seconds or less at most signals.

Signal Coordination 

Along major arterials which have a number of traffic signals spaced at periodic intervals, the traffic signals may be synchronized to provide coordinated movement along the major street. The timing is set such that vehicles traveling at the speed limit may meet the least amount of delay along the arterial.  These specially coordinated systems include all or some of the following streets:

• Stoneridge Drive (am/pm peak hours)
• Hopyard Road (all day)
• Santa Rita Road (all day and weekend)
• Stanley Boulevard (am/pm peak hours)
• First Street (am/pm peak hours)
• Sunol Boulevard (am/pm peak hours)
• Valley Avenue (pm peak hours)

Coordinating traffic signals helps the main street traffic flow but can cause some extra delay for the side street traffic.  During off-peak hours and late at night, most signals are taken out of coordination and run fully actuated cycling.

To have communication between the City’s Traffic Operations Center and the field equipment a combination of fiber, copper wire, and Wi-Fi are used. Data is transmitted using ether Ethernet or slower modems. The faster speeds of Ethernet allow the detection cameras, video cameras and signal controllers to be monitored in real-time, while the modems allow for monitoring with small delay.

Detection cameras point at oncoming traffic and place a call to the traffic controller to provide a green light. The surveillance cameras help in monitoring the traffic conditions around intersections to help manage the flow of traffic. Currently within Pleasanton there are 121 detection cameras operating at various intersections and four surveillance cameras.

A common myth of modern-day traffic signals lies in the use of cameras.  The City of Pleasanton is in the process of updating the detection system from induction loops in the ground, to digital cameras mounted on traffic signals and/or streetlights.  Detection is how the traffic signal senses whether or not a car is at the intersection.  The cameras are connected directly to the intersection controller equipment and are rarely viewed by City staff.  Video from these cameras is not recorded by the City.

The California MUTCD (Manual on Uniform Traffic Control Devices) dictates the location, size, shape and color of all traffic control devices.  The City of Pleasanton is required by State law to comply with the guidelines of this manual.  In this manual there are specific requirements that would indicate the need for installation of traffic signals.  These requirements include:

• The amount of vehicular and pedestrian traffic
• The need to provide interruption to the major street flow so that side street vehicles and pedestrians may enter or cross
• Special conditions such as hills, curves and vehicular speeds
• The collision history of the intersection

A new traffic signal costs in the range of $175,000 to $225,000.  Therefore, their installation must be carefully considered.  Traffic signals are installed using various funding sources, including your gas tax dollars, measure B funds (1/2 cent sales tax), developer fees and other special assessment fees

The City of Pleasanton maintains a traffic signal priority list to identify the locations with the highest need for a new traffic signal.  The purpose of the priority rating system is to impartially rank all intersections so qualifying. This rating is used to make recommendations for the installation of signals under various City improvement programs.  This system is based on warrants for traffic signals. Points are added and the intersections are arranged by descending number of points to form a priority list.  The conditions that are evaluated include: vehicular volume, interruption of continuous traffic, pedestrian volume, proximity to nearest signalized location and accident rate.  Click here for the current traffic signal priority list.

The Traffic Engineering Division requests that you contact us immediately if you suspect that a traffic signal is not functioning properly.  Your input is greatly appreciated.  If this occurs after hours and you think it is a concern that needs to be addressed immediately please call the Police Department at 925-931-5100.