The Traffic Engineering Section provides general traffic engineering support services, traffic signal system operations management, traffic signal system design, capital project management, traffic data collection, plan review for encroachment permits and capital improvement projects, sight clearance inspections, and responses to citizen inquiries and requests. The mission of the Traffic Engineering Section is to provide for safe and efficient traffic flow throughout the City.
|Mike Talley, P.E.
|Deborah Fehr, P.E.
________________________________________________________________________________________________Traffic Signal System Upgrades FAQs
Q: How do typical traffic signals work?
A: In general, traffic signals operate predictably. Someone who drives a corridor on a regular basis will know the order of every movement (phase sequences), have a sense of how long they have to wait for their turn (cycle length), and know how long their light will be green (green time). Cycle length and phase sequences are fixed based on a “time of day” plan. The City’s signals are programmed with minimum and maximum green times, which are triggered based on vehicle detection. Basically, traffic signals have been restricted to operate in a linear, predictable fashion.
Q: The traffic signal light patterns on some of the streets in San Ramon have changed. What’s going on?
A: In August 2010, the City deployed a new traffic signal system at the following 14 intersections on Bollinger Canyon Road and Crow Canyon Road:
|BOLLINGER CANYON RD||CROW CANYON ROAD|
The new system is not restricted to fixed cycle lengths and phase sequencing. The new system is designed to use all available green time as efficiently as possible, which means phases will be served out of sequence and cycle lengths are no longer fixed. This system automatically adjusts the traffic signal timing in response to actual demand. It collects traffic data through video cameras that are mounted at each intersection, and each signal is communicating with the adjacent signal using the real time data to determine the optimum intersection timing and sequencing to minimize stopping and delays.
Q: How much did the project cost and how was it funded?
A: The $1.2 million system is funded almost entirely through Proposition 1B Traffic Light Synchronization Program and Transportation Fund for Clean Air grants.
Q: When I was trying to make a left turn, the light changed more than once before I was able to make it through the light. What happened?
A: The new system serves vehicles as quickly as possible based on delay. This operation will result in a different experience for drivers who are accustomed to the traffic signals serving most of the vehicles each phase. Also, the system attempts to utilize available segments of green time, which may result in a portion of the waiting vehicles not getting served with the first green light. Generally, drivers should notice an improvement in their commute time, although some drivers may experience a slight increase in delay accessing Crow Canyon Road or Bollinger Canyon Road.
Q: Why was I skipped today? I saw another movement get a green light twice before I got a green light.
A: Since the new system is not restricted to operate sequentially, it will serve movements “out of phase” as it tries to use every available block of green time. This operation can initially result in confusion for drivers who are accustomed to the traffic signals serving each phase in a predictable sequence, and some drivers may conclude that they have been skipped. Generally, drivers should notice an improvement in their commute time.
Q: Are the new white video cameras on the traffic signal poles used by the Police Department for enforcement?
A: No, the new cameras are used exclusively for the new signal system to detect when a vehicle is approaching a signalized intersection. The images are not recorded or used in any way by the Police Department. Also, license plates are typically not legible in these cameras.
Q: Would it be possible to review video footage of a traffic incident yesterday?
A: No. The video footage is not recorded or stored, nor can it be recorded or stored.
Q: Why was it necessary to change traffic signal systems? The old one seemed to work fine.
A: There are several reasons for the change: 1) The main benefit of the new system is compatibility with Caltrans’ traffic signals. Currently, Caltrans’ signals operate independently and are not coordinated with the City’s traffic signals. The City is working with Caltrans to install the new system at the four I-680 off-ramp intersections on Bollinger Canyon and Crow Canyon Roads. The goal is to coordinate the operation of the City and State systems; and, once completed, the system is expected to significantly reduce stops and delays for the majority of drivers on Bollinger Canyon and Crow Canyon Roads. 2) As traffic volumes increase and decrease and traffic patterns change, traffic signal timing and coordination plans need to be updated. This is an expensive and time consuming process. The new signal system does this automatically on a daily basis.
Q: Why did the City Pay over a million dollars of taxpayer funds for a system that made getting in and out of my neighborhood more difficult?
Additionally, some increase in delay should be expected. As arterial traffic demand increases, side street delays increase as well. Synchronization on any arterial always results in some increase in delays for minor streets. This increase is generally accepted as an unavoidable side effect of synchronized operation. When operating properly, most users are likely to make up for the increase in delays as they should move through the arterial corridor much more quickly.
Q: Why do I see the people getting cut off because the green light is so short? Why do I see some people getting served with a green light twice while others have to wait?
A: There are a number of actions we can take to ensure that the green time is extended, but the unusual sequencing is part of the new system’s unique logic. An understanding of the theory behind the new system operation may help explain why it often serves out of the traditional order.
The new system counts the number of vehicles in each lane, and sends the data to a computer to optimize the allocation of green time. It attempts to follow a timing sequence that best serves the greatest number of cars, without regard to the traditional sequence. To accomplish this, sometimes it serves a movement twice while others wait. We learned that the system tends to overprotect the main street traffic priority at the expense of the side streets. Consequently, we have made major system changes to improve service for the minor streets.
Drivers will need to get used to the new operation, and to be alert for green lights outside of the customary sequence. We have adjusted the signals at Tahiti Drive and Twin Creeks Drive such that excessively short green lights should be rarely seen. We will be monitoring green intervals to confirm that our adjustments have been successful.
Any questions or comments should be directed to the City’s Engineering Service Department at (925) 973-2670.