Sustainable light rail consistency, interoperability and standardisation

Conventionally, light rail networks have been designed and constructed on an individual project basis, each with a unique design solution based around the type, model and platform of the Light Rail vehicle (LRV) proposed or delivered for the network.
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Sustainable light rail consistency, interoperability and standardisation

By Michael Uhlig, Lead Engineer Rolling Stock Access Integrity; Kenelm Wong, Senior Engineer Rolling Stock Mechanical Systems; and Jakub Zawada, Senior Engineer Rolling Stock Access Integrity.

Conventionally, light rail networks have been designed and constructed on an individual project basis, each with a unique design solution based around the type, model and platform of the Light Rail vehicle (LRV) proposed or delivered for the network.

Three new light rail networks are expected to be operational in NSW within the next five years. Given the geographic proximity of some networks and that of planned future networks, and their relative delivery timeframes, it is prudent to have consistency, interoperability and standardisation requirements in place to enable compatibility between them. The current absence of these requirements may prevent or constrain LRVs from interoperating on the Transport for NSW (TfNSW) Light Rail networks now and in the future. Interoperability also brings asset management and customer experience benefits and efficiencies.

The Asset Standards Authority (ASA) have, through working closely with light rail vehicle suppliers, light rail project delivery offices and other transport agencies, developed the minimum operating standards for Light Rail Units (Minimum Operating Standards for Light Rail Vehicles) (LRUs) based on a “network of networks” philosophy (see Figure 1).

Figure 1: ASA ‘Network of Networks’ philosophy 

The TfNSW Light Rail network

The Inner West Light Rail network, operating between Central Railway Station in the Sydney CBD and the Inner West suburb of Dulwich Hill, is the only currently operating route on the TfNSW Light Rail Network.

Table 1 provides a summary of the existing and planned Light Rail lines and Figure 1 and Figure 2 shows their alignments, forming the TfNSW Light Rail Network.

In 2016, following various discussions within TfNSW and with industry stakeholders the ASA began to develop a suite of light rail standards around the three key principles of consistency, interoperability and standardisation.




Inner West Light Rail


12.8 km

CBD and South East Light Rail


12 km

Newcastle Light Rail


2.7 km

Parramatta Light Rail (PLR) Stage 1


12 km

Parramatta Light Rail (PLR) Stage 2



Table 1: Existing and planned lines on the TfNSW Light Rail Network  Figure 2: Light Rail networks in Sydney  Figure 3: Light Rail network in Newcastle 

Development and assurance of the minimum operating standards for Light Rail

Initially the key principles and high level design parameters for the development of light rail systems were summarised in an ASA Technical Note in order to provide some basic requirements amongst projects and the industry. Upon further research, an internal ASA document was developed which set out the framework for individual light rail standard development.

Of the 17 rolling stock light rail standards scoped, four of them were classified as network interface standards and the remaining 13 were related to specific onboard LRV topics (e.g. electronic systems, crash worthiness and heating, ventilation, and air conditioning {HVAC}).


Transforming heavy rail concepts to meet Light Rail objectives

The four light rail vehicle network interface standards provided a set of minimum operating requirements that are performance/function based. However, at certain interfaces the requirements or elements need to be prescriptive, in order to meet an acceptable level of interoperability and consistency across the network.

In heavy rail, the Minimum Operating Standards for Rolling Stock, commonly known as the RSUs, have been used to achieve interoperability of different rolling stock types across the TfNSW heavy rail metropolitan network since 1997. This concept was adapted for the Light Rail standards.


Light Rail Vehicle (LRV) manufacturers’ standard products

While it was important that the LRVs achieve vehicle interoperability across the TfNSW Light Rail network, it was also important that the requirements prescribed in the standard do not preclude different suppliers from offering their own products/platforms and constrain suppliers to offer the same products as each other.

Through ASA’s engagement with LRV suppliers and TfNSW Light Rail project teams, key interface design information describing the standard LRV platform from three of the world’s largest LRV manufacturers was analysed to formulate minimum requirements.

In addition, using the engineering documentation from the Inner West Light Rail and CBD and South East Light Rail projects, a LRV infrastructure interface review was conducted to ensure requirements prescribed in the LRVs cater for future networks and maximises interoperability between existing networks.

Governance: Light Rail Technical Working Group

In order to coordinate the input of different stakeholder groups within TfNSW, a Light Rail technical working group was set up by the Asset Standards Authority with all light rail standard drafts  circulated for comment, in addition to the individual stakeholders  identified and consulted relevant for each standard (for example LRV manufacturers).  Coordinating the input of different stakeholders was important to ensure consistency and interoperability across the networks, ensuring that stakeholders directly impacted by the light rail network  were informed and could fill any gaps in knowledge. The key members on the working group represented the following areas in TfNSW: Centre for Road Safety, CBD and South East Light Rail Project, Parramatta Light Rail Project, Roads & Maritime Services and Transport Planning.


Interdisciplinary collaboration

Stakeholders in the Light Rail technical working group were engaged according to their expertise in various disciplines. Table 2 provides a high level summary of the topics covered as part of the interdisciplinary collaboration.


Examples of interface topics


Track geometry; track forces and stresses; wheel rail interface


Bridges and structures loading


Overhead wiring and pantographs; vehicle borne electric protection

Rail Signalling

LRV detection; EMC; LRV braking

Road Traffic Signals

Road intersection interface between LRV and intersection traffic signals

Table 2: Summary of interdisciplinary coordination of topics.

Working relationship with Parramatta Light Rail (PLR) Project

In addition to the engagement with the PLR project team at a technical working group level, the ASA rolling stock team have established  value-adding working relationship with PLR's engineering team and its technical advisors to ensure that the light rail standards were 'fit for purpose' on a project scale. From the open and frequent discussions between ASA and PLR, both parties were able to gain confidence that the proposed standards met the project requirements and that the project as designed and commissioned would be compliant to the standards. The LRVs captured the lessons learnt from other Light Rail networks and embedded whole-of-life cost and resourcing considerations into the requirements as a result of some technical advisors’ experience as an operator/maintainer.

Collectively this working relationship provided the assurance that the LRVs were developed under the key principles of consistency, interoperability and standardisation set by TfNSW.


Working relationship case study: Gaining consensus on step and gap recommendations

In terms of light rail, considerations will always have to be made for a step (vertical clearance) or gap (horizontal clearance) between the rolling stock and the platform. Relevant stakeholders on this topic gathered together to discuss the requirements relating to the step and gap. Their considerations (Table 3) were collected and upon further research on step and gap recommendations from different literature, it was determined that with the existing technology available a 20 mm step and 40 mm gap is considered to be appropriate and acceptable values for unassisted boarding in a light rail environment. These step and gap values were then translated into platform height and platform width of 300 mm ARL and 1395 mm from centre of track respectively in the light rail track standard.

Stakeholder group

Key considerations

Customer Experience

Consistent alighting / boarding experience on the TfNSW network

Disability Compliance

Maximise opportunity for unassisted alighting / boarding ; Compliance with DSAPT

Human factors

Trip hazards; Predictability for customers

Rolling Stock

Prevent LRV hitting the platform due to kinematics


(Track, building & stops)

Meet with the safe entry and exit requirement of passengers; Minimise the risk of LRV coming into contact with the platform when approaching or departing a station due to track tolerances

Table 3: Summary of the step and gap considerations when developing the LRUs

When the PLR project was engaged and advised of the platform height and width values proposed, the PLR technical advisors were initially doubtful. However, after explaining how the values were derived and from having a strong working relationship built on trust and mutual respect of each other’s expertise and knowledge, the project team was satisfied with the parameters and the rationale behind them.



The development of the light rail standards was an attempt to open up the TfNSW Light Rail network to future development without limiting it to a particular design solution. Interoperability considerations and the concept of a “network of networks” applied during the development of the standards has led to a higher likelihood of achieving light rail consistency, interoperability and standardisation in a sustainable manner through:

  • Shared maintenance facilities in the future
  • Wider opportunity (choice of products) for future procurement
  • Economies of scale in future procurement
  • Ensuring optimal participation of LRV manufacturers in future procurement

In many instances, while it is technically feasible to modify both the LRV and/or the infrastructure in the future to achieve full interoperability, the final decision will need to be justified by a cost benefit analysis conducted during future network development. Therefore in order to maximise sustainability for light rail in NSW, a well-defined and transparent concept of operations for the network should be available and periodically reviewed as new light rail projects emerge and would normally call for a specified degree of interoperability that meets business and customer needs.



The light rail standards development and assurance process maximised opportunities for interoperability on the TfNSW Light Rail network and met the TfNSW consistency theme through providing requirements that allow equal participation by LRV manufacturers, present and future.

To further enhance sustainability of light rail systems, transport planners will need to integrate and manage the concept of operations for the whole TfNSW Light Rail network from each individual Light Rail projects' concept of operations. The Light Rail working group initiated by the ASA through its engagement with relevant stakeholders from LRV suppliers and TfNSW subject matter experts will play a pivotal role in managing the consistency, interoperability and standardisation of all aspects of the Light Rail network.



The authors acknowledge the support of the light rail vehicle manufacturers and technical advisors on the Parramatta Light Rail project on their active involvement in the development of the LRVs.