How many traffic signals are in the Township?
Who owns and maintains the traffic signals in the Township?
Currently there are 20 traffic signals, a flasher at the bottom of Pine Grove Mountain at the intersection of Water Street and Pine Grove Road, and the Ferguson Township Elementary School Speed Limit Flasher. The Township also reimburses State College Borough for one half of the expenses to operate the signal at the intersection of Blue Course Drive and Whitehall Road that straddles the municipal boundaries.
These are all electronic traffic control devices installed under permit by the Pennsylvania Department of Transportation (PennDOT). There is also a recently issued permit for the installation of a planned traffic signal at the intersection of Blue Course Drive and Bristol Avenue.
How is a vehicle detected at a traffic signal?
Ferguson Township owns, operates, and maintains all of them by permit with PennDOT.
Our Public Works crew performs basic annual inspections of the signal cabinets, junction boxes, signal heads, push buttons, signs, detectors, and more. We replace the LED signal indications every seven years and replace the batteries for the Uninterruptable Power Supply (UPS) every five years. The cabinet at each intersection contains controllers, relays, and computer equipment that must also be maintained and updated.
What is a loop detector?
Various devices are available to allow a traffic signal controller to know when a vehicle is approaching or waiting at the signal. These devices are called detectors. The common types of detectors used in the industry are loop detectors, video cameras, and radar.
How does digital radar work?
The most common and historically used detector is an in-pavement loop detector. This technology has been around the longest. These type of detectors consist of a wire that is cut into the pavement in a loop form to create a large inductor in the street. When a large metal object passes over the loop, a drop in the inductance occurs that is sensed by an amplifier in the cabinet. This amplifier also translates that drop in inductance to an input to the controller to let it know that a vehicle is there.
Why is digital radar better than loop detection?
Digital radar uses radar heads mounted to the traffic signal poles and arms. These heads use a radar arrays that sense the presence of objects within the designated area of the radar. The radar is able to constantly track the objects within the radar array and also identify the objects' speed and anticipated arrival. This information is then sent to the controller to let it know where the vehicle is and when it is anticipated to arrive at the intersection.
Radar detector is reliable and not susceptible to damage from pavement degradation or street excavation. In-pavement loops can fail from freeze/thaw action -- creating cracking that breaks the wires. Potholes, pavement patching, utility excavation, or milling and repaving a street will also damage the loop detector wires and require replacement.
Secondly, the digital radar detector continuously tracks a vehicle along its approach to the signal, instead of just sensing a vehicle at one location, as the loop detector does. This continuous tracking allows the controller to know when the vehicle will arrive instead of estimating its arrival time relative to the posted speed limit. Knowing when the vehicle will arrive helps to hold the green light as necessary, helping to reduce the incidence of "dilemma zone," the moment when a driver approaches a signal and needs to decide whether to stop or continue through the yellow light.
Lastly, the digital radar device is capable of detecting not only vehicles that are large enough to create a drop in inductance at a loop detector, but also smaller objects with less metal, such as motorcycles and bicycles. All of these features make the digital radar better than loop detection.
What causes traffic signal timing to be too short, take too long to change, or stop working altogether?
Who repairs the Township’s traffic signals in the event of a power outage, crash, or other interruption?
A number of factors can cause traffic signals not to operate efficiently.
During construction season, road work can result in traffic taking alternate routes to avoid construction delays. This can add traffic to locations where it is not anticipated and create additional delays at traffic signals along that route. Also, construction excavation in the roadway can create failed detectors that the traffic signal relies upon to operate efficiently. For example, many vehicle detectors on North Atherton Street are out of service due to excavation and therefore the signals are not operating as efficiently as they are designed until new detectors are installed.
New developments increase traffic and can also change traffic patterns as new streets are connected. Periodically the Township will evaluate the changes in traffic and revise the timing of the traffic signals to respond to these changes. These efforts need to be approved by PennDOT as revisions to the traffic signal permit.
Some traffic signals along North Atherton Street, Blue Course Drive and Science Park Road operate in coordination with each other during certain times of day to keep traffic moving along the corridors and limit the number of stops. To do this, the intersecting streets must wait longer than normal. The times of coordination vary by corridor.
Another operation that can create a shorter than normal green time is the transit signal priority system that operates along North Atherton Street. CATA buses are equipped with devices to extend the green time for them. This extra green time is allotted from the side street green times on alternating cycles.
Traffic signals that are completely out of service are normally caused by extended power outages or vehicle accidents. These occurrences are rare and get immediate attention to be resolved.
Fun Fact: By the end of 2019, every traffic signal in Ferguson Township will have an Uninterruptible Power Supply (UPS). If the power goes out, the UPS will continue to operate the signal for approximately eight hours. But if no one reports the power outage, the UPS energy could run out, as it did on one occasion at the intersection of Martin Street and Blue Course Drive.
The traffic signals with UPS have power source indicators that are located on the side of the traffic signal cabinet, as depicted in these photos.
Photo at Top: Green is good
Photo at Bottom: Red is bad
When we get a call or complaint, Ferguson Township Public Works will respond and repair the signal ourselves if possible. If the extent of the issue is beyond our capabilities, we have an on-call contractor who is contacted to assist in the repairs. Minor non-critical issues are normally resolved within two days, and emergency issues that require immediate attention to assist police have a two-hour response time.