• Reliability - The Control Centre must operate reliably and in a predictable manner. The possibility of system failure must be minimised.
• Cost Effectiveness - Although the savings of centralisation are significant, a cost effective solution must be implemented to maximise return on investment.
• Functionality - The Control Centre must have available, as a minimum requirement, the features available in the systems it is replacing, and at best significantly improve on such features.

REALFLEX SOLUTION:

Specifications
From this a full system specification was developed which outlined the following requirements:

• Use of standard IBM compatible personal computers for servers and workstations.
• Operator interface via VDU and point device (e.g. mouse).
• Any Local Area Network (LAN) linking workstations must be industry standard (e.g. Ethernet) and TCP/IP compatible.
• Capable of communicating with existing field equipment which meet current CCITT recommendations for protocol and communications interface.
• Capable of communications over a variety of media including fibre optic and copper, leased and dial up.
• Expandable up to a minimum of 16 workstations in a modular fashion.
• User programmable with Tranz Rail staff able to enter database and create graphic displays.
• Alterations to system database and graphic displays possible without rebooting system.
• Servers able to operate in hot standby mode with automatic failover if failure of online node detected.
• The ability for Tranz Rail staff to create macros for simplifying common control functions (e.g. crossing trains). The software chosen was Realflex 4.

Operator Interface
The operator interface was developed in conjunction with the Train Control Operators who use the system. Although it was difficult at first for the operators to relate to VDU layouts and operation with a mouse after years of operation with push buttons and a mimic panel, this was an important part in the development of the system. Involving the operators at this stage gave them some "ownership" of the finished product and also a feeling of control over their destiny.
As a result of this consultation the screen layouts were developed with the following criteria:

• Operators must be able to "see" and control the entire section of railway they have control over without having to navigate between screen layouts.
• Control of signals achieved by pointing and clicking on the appropriate signal head representation with a mouse.
• Control of points achieved by pointing and clicking on the appropriate points number.
• Where applicable, alarms and operator prompts should flash on the screen to alert the operator.
• The screen layouts must be large enough to avoid unnecessary eye strain.
• The lie of points will be indicated by a yellow line that turns red when occupied by a train.
• Signal aspects will be green for clear and red for danger.
• Track segments will normally be black and will show red when occupied.
• Miscellaneous indications (time delays, barriers, etc) will appear on the screen when active.

Automated Procedures
One of the major advantages of a computer based office is the ability to reduce operator workload by automating repetitive tasks. Realflex has Control Sequence Language (CSL) which allows controls to be issued automatically when initiated by the operators. CSL enables procedures to be written which can monitor field events (indications) and issue controls without specific operator intervention.
A number of CSL programs have been written which automate some operator procedures and thereby reduce operator involvement in the system. Examples of CSL programs are the automatic crossing of trains, the automatic routing of trains through double to single line stations, the automatic turning of locomotives on a triangle and the clearing of all signals in a specified direction through a station. In each case the procedure is initiated (and can be terminated) by the operator but any further intervention in the procedure is not required.

System Security
Security is achieved by requiring operators to select the area(s) they need to control. Once this is done all stations in the designated area are under the control of that operator and any attempt by other operators to control those stations will be denied.

Communications
The Signalling and Train Radio Systems originally grew as network nodes around what was previously distributed Train Control offices. As these offices were progressively closed as part of the centralisation process it was decided to leave these nodes basically intact and install interfacing equipment to allow remote control of the systems from the central point, the National Train Control Centre (NTCC).
Tranz Rail owned and maintained its own fibre optic transmission network (FOTS) so "leased" circuit capacity is readily available between node points and the NTCC. This capacity is generally in the "backbone" network through the centre of the country. Because the nodes are located along this backbone, circuit provision is made easier. Within the nodal areas, the distribution of Signalling multidrop circuits was achieved by using either Tranz Rail owned copper cable or if this was not an option, a service provider was be used to supply "leased line" circuits. The Train Radio network within each nodal area is comprised of a series of linked hilltop repeater sites with radio coverage provided, via specialised tunnel radio systems, through tunnels longer than 100 metres. There is diversity in the communications path options available between node points and the NTCC. The main path is the "leased line" available via the FOTS. The other is via the PSTN network, and allows for automatic dialup operation should the "leased line" fail. This provides redundancy for the Communications circuits and therefore minimises the risk of a node point not being in contact with the NTCC. Dial up operation with each node point effectively allows control from any location which has access to the PSTN network and forms the basis for the disaster recovery plan.

System Reliability and Availability
Of major concern with any centralised control system is overall reliability as any failure has widespread effects. The design of this system with dual redundant ethernet networks, online and hot standby computers and workstation switching flexibility has minimised the effects of any single failure on the system as a whole. Redundancy in the communications links and the nodal communications network mean that any single communications fault will not prevent system operation. This feature has been used on occasions when the main communications link has failed.

RESULTS:

Train Control systems have developed over the years to the point where large scale centralised control is attractive and viable.
Tranz Rail utilised "off the shelf" control systems products and PC based technology to develop a cost effective and functional train control system which has the ability to expand in order to meet the needs of the future. Particular attention has been paid to the reliability and availability of the system especially with regard to LAN communications, main processing CPU's and communications links.
Realflex and QNX have responded well to the rigors and processing requirements of a Train Control system. The Train Control centralisation project has been challenging, and the end result is a positive reflection on all involved, including all Train Control Operators who have used and commented on the system.

REALFLEX SYSTEMS SOFTWARE:

Realflex, Flexview.

DATABASE SIZE:

12,000 points

PC HARDWARE:

Various computers