Yes, no, when, where – the tram-train conundrum

Part one: What is a tram-train? Why and when would you need one?

1.1 Context

We live in an increasingly connected world. People want to, and can be, connected in all aspects of their lives. Travel is a key enabler for physically interacting with others. The recent Covid-19 pandemic may have changed travel patterns, but evidence proves that the desire amongst people of all ages to engage and meet with others both in a professional and leisurely manner, and the important role this has to play in everyday life, continues.

Rail, and public transport generally, is a versatile, flexible solution to local and suburban connectivity. Tram-train schemes have a role to play in providing flexibility for future travel needs. A tram-train is a vehicle that can travel on both a tram network and a conventional rail network. This enables new routes to be introduced, providing continuous journeys connecting tram stops with conventional rail stations, predominantly by running tram-train vehicles on existing tram and rail infrastructure. Without the constraints suffered by ‘heavy rail’ traffic, this versatile transport system is able to reach areas of both dense and sparse population, from housing areas to business districts, whilst helping decarbonise transport, and deliver social value.

Like any transport technology, tram-train needs to be implemented appropriately for the full benefits to be realised. While tram-train schemes are no longer novel, they are far from widespread in their usage. So, in this three-part blog series, we discuss some of the key factors that steer decision making for tram-train schemes. In part one, we consider when to use tram-train systems, and some factors and risks that drive the decision making around usage. Part two will look at sample routes, operations, and technology; and part three will examine driving prosperity through procurement and social value.

There is considerable interest in tram-train schemes across Great Britain. To illustrate the topics, we have utilised the progress being made by South Wales Metro, and wider Transport for Wales (TfW) initiatives, but the underlying factors are relevant to most jurisdictions and organisations considering schemes for tram-train.

1.2 Why tram-train?

Tram-trains have become commonly referenced as a solution to public transport conundrums. However, tram-trains are only the right solution in specific circumstances.

  • If the transport route is on a mixed-use heavy rail network, a heavy rail train is the solution
  • On a segregated rail line from which heavy rail traffic is barred, metro or light rail is the solution
  • For optimum integration within on-street settings predominantly, tram is the solution
  • Only where existing mixed-use heavy rail combined with a light rail network or on-street running is required is tram-train the solution.

For example, in Manchester, when the opportunity arose to take over under-used heavy rail routes, the decision was taken to procure the heavy rail line and convert it for tram usage, thus reducing the need for heavy-light rail interfaces and compromises, which a tram-train solution would have required.

Invariably, the new route part will be a reclaimed alignment of a heavy rail route, long since lifted, or else a brand-new alignment threaded amongst existing street and urban infrastructure, connecting to existing heavy rail route parts leading to relatively local destinations, or potentially to other new route parts.

Are there some local services that you know of that might offer major increases in connectivity for an area through relatively modest excursions from the heavy rail route into centres of population and business?

1.3 Preventing route and technology driving risk

Significant increases in programme cost and duration can be driven by the choice of route, and technology factors. However, if these factors are considered early, and particularly in combination with route optioneering, then the maximum opportunity is derived to minimise their effect on cost and programme, and perhaps some of the risks may be avoided entirely.

These factors are particularly sensitive to tram-train operations, since they must accommodate different rail systems. However, if a light rail system is taking over a disused or underused heavy rail route, some of these factors will also apply.

Experience has revealed some notable risk factors that require specific consideration, including:

  • interfaces between networks; including boundaries for electrification, operations, maintenance and signalling;
  • mixing tram-trains with other heavy rail vehicles, which introduces concerns around increased speeds and subsequent crashworthiness and mitigations;
  • electrical clearance with infrastructure along the route, including overbridges, platforms, canopies, signals and signage, which can result in significant cost escalations;
  • AC/DC interfaces introducing the need to manage or prevent stray currents;
  • low level platforms, which introduce risks related to trespass, heavy rail gauging, and heavy rail aerodynamic effects;
  • different wheel / rail profiles, which can cause excessive wear or poor riding characteristics; and
  • different track standards such as gauge widening (common on heavy rail but, not on light rail).

There can also be organisational issues that affect risk, such as where a scheme is extended, and there is a change in the organisations involved originally, or where one major system component (such as a rolling stock product with its inherent capabilities) has not been chosen. Such factors can mean keeping interfacing safety and performance requirements of various systems in pace with one another can be difficult.

Is there a tram-train deployment that has solved the multi-organisation and multi-system risks effectively, in your view, and could be held as an exemplar?

1.4 Building on these factors in part two

Cognisant of these factors, in the next part of this discussion, an example is worked through of an imagined extension of the South Wales Metro scheme, and demonstrates where the tram-train concept can generate significant value; both in providing a passenger transport system, and additionally in providing much needed social value and prosperity to the areas served.