Tim Hall on optimising emergency and public transport traffic signal priority control system operations.
Priority control systems, whether vehicle, central control or intersection based, are all composed of hardware devices running software programs. These devices may include (but are not limited to) signaling emitters, signal detectors, intersection communications devices, and assorted supporting devices.
The traditional use of priority control has been to implement emergency vehicle preemption (EVP). It is now becoming much more common for municipalities to operate Transit Signal Priority (TSP) systems in conjunction with EVP operations. The ideal system allows the users of both types of system to leverage and use the same intersection and central office hardware and software.
Emergency vehicle priority preemption of normal traffic signal operation provides safe rapid progress for authorised emergency vehicles through priority control equipped intersections. If an EVP request is forwarded from a vehicle or agency to the intersection controller, when this is approved a green light is applied to the requested traffic signal phase. Since this detection occurs in real-time, and by the nature of the request priority, there is little chance that emergency vehicles will be denied a green light. This ensures their efficient onward journey, and minimises the risk of accidents involving other vehicles at the intersection.
One consequence of EVP control of traffic signals is some level of disruption to signal timing and coordination. This may lead to undesirable system operation until timing and coordination recovery routines can be implemented. But proper configuration of the priority control system, especially using estimated time of arrival at the intersection such as Global Traffic Technologies’ Opticom™ system employs, can allow the controller to recover normal coordination within one cycle.
Working with Transit Signal Priority
Increasingly transit signal priority, in which a requesting vehicle, usually a bus, requests either the extension of an existing green or the delay of an imminent red phase, is being used by public transport agencies as an effective method to maintain schedule adherence or headway status.
TSP operation is usually less impactful to coordination or timing in most applications but can benefit from centralised management in terms of maintaining its effectiveness in the presence of EVP users of the system.
One of the biggest challenges facing traffic engineers is providing all of the benefits of interoperating EVP and TSP solutions to emergency service and transit providers, while at the same time minimising the impact to overall traffic operations.
Past methods to minimise the impact of priority control on signal timing and coordination have relied upon an intersection-by-intersection optimisation approach. This approach is both expensive and difficult to modify for changing needs and conditions.
Utilising Central Management Software
The best approach to configure, monitor, and maintain a unified TSP/EVP solution is through the use of Central Management Software.
Primary areas that may be optimised for TSP include;
- System operations
- Optimisation for headway, or schedule adherence
- Transport of large numbers of people into or out of an area
- Time of day plans
- System performance reports and monitoring
- Merged compatible data from various priority control types.(Infrared, GPS, Centralized)
- BRT, and TSP and EVP operations with the same system
- Special operating modes for both planned and unplanned major events
Flexible system operations
The ability to vary TSP operation by time of day, or by calendar dates, provides many advantages to system operators. Peak ridership times or days may be specified for special lane treatment. Alternately TSP can be modulated, or even disabled, to maximise signal coordination during desired periods.
The best way to accomplish this feature is through a CMS program communicating with the intersections from a central office. Time plan updates may be downloaded to the intersections quickly and efficiently if changes are desired. Monitoring reports provide insights into the performance of the system, and can be used in time plan development to further fine tune system operation.
Central Management Software also allows system operators to optimise either headway or schedule adherence performance by adjusting control parameters for the different intersections on routes to provide desired results. Updates may be carried out frequently without the need to contact moving vehicles.
Coordinating BRT, TSP and EVP operations
Central Management Software allows system operators to accommodate the needs of EVP, TSP, and Bus Rapid Transit (BRT) operations by facilitating the configuration and management of intersection priority control for optimum settings in each case.
There is no need for multiple priority control systems as the ability of sophisticated priority control equipment to switch between modes may be utilised efficiently and without the need for duplicated infrastructure support.
Special operating modes for major events
A well-designed monitoring application should also extend true priority control capabilities to Transit when required. Typically low priority control is used to extend green lights rather than change them from red to green. There are times, however, when something more is required.
Large events are often served by park-and-ride vehicles that transport many attendees efficiently. If these public transport vehicles are equipped with priority control devices, CMS can cause red lights to turn green when they approach. However, if a high priority vehicle requires the other approach, it will override the in-progress priority control and give it to the emergency responder.
This capability is also useful for disaster evacuation and can qualify the implementing city for grant money. Event and disaster evacuation plans may be set up in advance, ready to implement at the touch of a button. Alternatively, they may be scheduled for implementation at specified times and dates, yet may be cancelled if required.
System performance reports and monitoring
Getting the right information to the right department is the most efficient model for optimisation. Central Management Software can turn on-screen visual alerts into email or text messages. Remote support personnel may even access the affected intersection though secure laptop, mobile phones, or other mobile devices. Both notification and access can be improved to such a degree that intersection priority control downtime is virtually eliminated.
When monitoring is performed in real-time there are other advantages: some advanced priority control systems such as Opticom™ can show exact vehicle positions and their priority control status on dynamically updated maps. High-level tabular displays can allow the correlation of dispatch tickets with priority control usage.
The use of individual vehicle identifiers allows systems managers to authorise, monitor, and report on who is using the system at any given time. Similarly, patterns of priority control can be identified when graphical interfaces display the data in a comprehensive, high-level manner. Major accidents, emergencies, and in-progress disasters are easy to spot at a glance. This raises awareness and assists in resource deployment, making the best use of finite response resources.
Less dramatic, but just as useful, are reports that identify priority control issues, trends, and usage. These are based on logged priority control data and results are available at the touch of a button. These pre-configured reports may also be scheduled as email tasks destined for end users, requiring no action on their part.
Again, awareness is raised and efficiency increases when proactive monitoring software is in place. For those with billing agreements in place, as in the case of a congestion charge, the Agency Usage Report allows for accurate billing of users based upon their actual usage.
Merged data from various priority control types
It sometimes happens that adjacent municipalities or agencies have installed and are operating different types of priority control equipment. Community A may have an optical priority control system while Community B uses a GPS radio-based solution.
In the EVP arena, the ability for agencies to provide mutual aid capability is important to public safety. In the case of TSP operations, public transport systems often operate over multiple political and jurisdictional boundaries, each of which may have existing priority control infrastructure.
One key to successful interoperability is hardware that can interoperate with multiple preemption technologies. The other equally important factor is the ability to leverage that existing infrastructure in an efficient effective manner.
Optimal system management and control can be obtained by using a central management software program capable of providing asset management and data processing for both systems through a common database and user interface. The ideal application should be able to provide the system user with reports, configuration utilities, and a monitoring capability that provides a seamless look and feel regardless of the type of priority control being utilized. The key here is user experience – seamless interoperability means more efficient operation.
In this case, Central Management Software provides an ideal means of configuring, maintaining, and monitoring this equipment so that optimal priority control operation, with minimal signal timing and coordination disruption, is achieved.
Centralised management enables remote control of security and mutual aid parameters. Priority control systems are by their nature distributed, with intersection and vehicle components spread throughout the city. Keeping unauthorised users off the system is easily accomplished, but what about appropriate access by valid users?
Mutual aid agreements allow communities to make the most of scarce emergency response resources. Priority control allows these far-flung resources to reach the scene quickly, and seconds saved make all the difference. However, mutual aid agreements do change, and this requires the priority control end-points be updated. Central Management Software performs these updates with a mouse click, whereas non-managed systems require costly, manual procedures be performed at each intersection.
As noted earlier, reports are crucial to identifying issues, but they also highlight optimisation opportunities. If fine-tuning system parameters means visiting the intersection in question, chances are the optimisation will not occur in a timely fashion. With reduced staffing it may not occur at all. Centralised configuration allows for easy, fast optimisation, plus the ability to monitor results. Changes may be reversed if they do not have the intended effect. This is possible with a Revisions capability that clearly shows what changes were made, by whom, and when.
Compliance initiatives are demanding that assets be tracked precisely and in a centralized manner. Centralised management software allows for automated asset management including depreciation, warranty, or deployment tracking.
GTT’s experience is that CMS provides the key to the successful, optimised interoperation of EVP and TSP systems: it offers minimal traffic disruption, and lets the traffic engineer manage, monitor and maintain the system from their desktop.
Timothy Hall is Market Development Director at Global Traffic Technologies