Signal Priority System

An Advanced Signal Priority System with No New Infrastructure Requirements

Introducing a novel signal priority system that supports Transit Signal Priority (TSP), automatic Pedestrian Signaling (PedSig), and a variety of other applications without requiring the acquisition and installation of additional capital infrastructure, including roadside equipment such as special-purpose optical or radio-frequency devices or DSRC installations. SPS also provides dramatic deployment time-savings for cities. The system’s key innovations are its use of existing infrastructure (including the public cellular network and the city’s Traffic Management System (TMS) and traffic network) to securely provide these capabilities, its use of mobile devices to request action from the signal network, including pedestrian walk signals, and its software-defined nature that supports extension and modification of capabilities without requiring hardware modifications or field-service modifications.

Transit Signal Priority

TSP can be provided using a combination of a background application running on cellular-connected mobile devices, applications running on servers in the cloud, and capabilities provided by the systems already running on existing controllers deployed in the city.

The onboard tablet, which is provided with a unique cryptographic certificate for authentication, determines vehicle position, heading, and speed and, in cooperation with the cloud-based server, determines which signal is being approached. The server uses models built using machine learning applied to data collected from previous trips to estimate when the bus will arrive at the signal based on a variety of factors. The server also has access to information on the current and predicted state of the signal in question. If a TSP request is in order, the server informs the appropriate controller via the V2If and the existing signal network that a bus is expected at the calculated time.

The system can utilize software already deployed in the controllers with the ability to implement an early or extended green, or manage specific change requests directly, to reduce the average signal delay for buses traveling through signalized intersections. The software also returns the controller’s response to the request, which can be used for system monitoring, or relayed to the bus to tell the operator about the expected state of the upcoming signal, as desired.

Automatic Pedestrian Calls

Another new capability lets pedestrian’s smart phones automatically generate walk requests.

A pedestrian running the PedSig app can enter a destination and begin to walk along the provided route. When they approach a pedestrian signal along the route, a request is sent to the cloud-based server indicating the crossing(s) that are desired. If the signal will be in the “Don’t Walk” state when they arrive, the server forwards a pedestrian call request to the appropriate controller, which treats it the same as a crosswalk button push. If the pedestrian has to cross in both directions, the system is capable of determining which order of crossings would be most efficient given predicted signal behavior and responding accordingly.

Alternatively, the app can simply observe the pedestrian’s progress and make an appropriate ped call in the direction of travel as they approach an intersection. The system uses information about the pedestrian’s speed, location, and track, as well as predicted signal behavior, to determine which–if any–call to make. If the pedestrian crosses the street or moves away from the crosswalk, the request can be canceled if not already serviced.

V2I Without New Infrastructure

As the leading provider of real-time, predictive, traffic-signal information, Connected Signals has worked with municipalities and other agencies to connect traffic signal infrastructure to vehicles and make reliable traffic signal information available to drivers for years. Real-time traffic signal state information is securely exported to the cloud from the TMS using our V2Iappliance. We then use proprietary techniques to build highly accurate predictive models for each of the City’s signals. Servers in the cloud support a variety of V2I ranging from red light countdowns and green-wave speed advisories to various types of analytics.

Now we have developed the capability to offer traffic signal solutions involving two-way communication between the cloud and city traffic systems. The V2If architecture has been enhanced to support cryptographically secured two-way communication. This allows outbound transmission of signal data and receipt of inbound requests from duly authenticated devices in the field, such as transit buses, while protecting the integrity of traffic systems.

To ensure the integrity of the traffic network, all apps allowed to make requests are cryptographically signed and communications are encrypted. The TSP app deployed on buses also requires individually provisioned cryptographic certificates to prevent unauthorized access. These safeguards, as well as security safeguards built into the V2If, prevent spoofed requests and malicious intrusions.

Future Enhancements

Because the system is largely software defined, new capabilities can be provided simply through software upgrades and the deployment of new or modified apps. These include but are certainly not limited to:

  • letting cyclists automatically make a “vehicle” call approaching a signal without having to push a button or “dance” around the loop detector, and receive an acknowledgement that the signal knows they’re there,
  • prioritizing cyclists (at an appropriate priority relative to transit and other vehicles),
  • providing “virtual” loop detectors at intersections between major roads and minor side streets to make the signals more responsive when cross traffic arrives,
  • providing priority to highly occupied or electric vehicles (popup HOVE lane), and
  • providing  EMS preemption.