The virtual world may appear far removed from the harsh reality of railway operations – brake dust, wheel squeal, night shifts. But the clean digital world of 0s and 1s is increasingly becoming a normal part of project delivery because of the benefits it offers for safety, efficiency and accuracy.

BIM and BIMwash

The current hot term is BIM: Building Information Modelling. The concept is that an asset has a digital life in addition to its physical life, and that information about the asset can accompany it from cradle to grave. In theory this should reduce rework by removing the paper interface: no more re-drawing based on old scanned copies.

The government has mandated that publicly procured projects must adopt the so-called BIM Level 2 by 2016. This has generated an industry in its own right looking at delivery of BIM and a consequent multiplication of jargon on the subject, to the extent that it risks becoming incomprehensible to an outsider.

The term ‘BIMwash’ is not some new and advanced kind of screen- cleaning fluid; rather, it relates to the inflated, deceptive or uninformed claims made about the use or performance of BIM.

Digital life, digital legacy

Parsons Brinckerhoff has been using BIM and similar processes for many years in the United States, on infrastructure projects such as the San Francisco-Oakland Bay Bridge and Seattle’s Alaskan Way Viaduct. In the US, alternative terms including Virtual Design and Construction (VDC) and Civil Integrated Management (CIM) are in general use.

In this country, Parsons Brinckerhoff has worked with digital modelling techniques for many years in the buildings sector and has been one of the leaders of transferring this expertise into the rail sector, on projects including Crossrail South-East section and Northern Hub.

fig 13 archive drawing

Partly in response to the overuse of the BIM term and associated BIMwash claims, Parsons Brinckerhoff has developed a lexicon of digital life, digital legacy and digital toolsets. The focus is on the digital outcomes which will be most useful to a client on a particular project, and which digital tools can be used most effectively.

Asset life

A further key factor with infrastructure projects is the interface with existing infrastructure. Much railway infrastructure dates from the 19th century. This interface is a critical one for the 3D model, and models need to be built of the existing structures before the new works can be digitally constructed alongside. This can be a significant and fundamental part of the ‘new’ design process.

One of the aims of BIM is to provide a digital life to ensure continuity of asset records. In the longer term, if this aim is fulfilled, then the need for modelling existing assets could reduce. However, the extent and maturity of the existing infrastructure in the UK are likely to make this challenging in practice. Many of these existing structures have an extensive pre-digital life including modifications, maintenance and change of use; there are many examples of viaduct structures which have already been widened two or three times.

Information about existing assets can be gathered from various sources, ranging from traditional archive drawings and intrusive investigations to modern laser surveys. The former remain invaluable for verifying hidden details that are unobtainable by laser surveys, such as arch ring thickness, waterproofing details or abutment construction. In some cases the record drawings can also reveal what can never be revealed by laser-scanning: the thought process and rationale of the original designer.

A key benefit of using digital techniques is the reduction in trackside access required for design surveys; this provides obvious safety benefits. Likewise, linking the digital model to a schedule, adding the time dimension and moving to 4D, allows the construction sequence to be rehearsed digitally and potential risks identified. Efficiencies can be gained by adding cost information, 5D, to allow costed bills of quantities to be produced from the model and updated rapidly.

Culture and technology

The successful adoption of BIM is more about cultural change than technological enablers. Much of the technology has existed for some time, such as information servers which provide a common data environment. However, shared data is just one part of a wider collaboration and Parsons Brinckerhoff sees a trend towards co-located working and alliances as part of successful project delivery.

The BIM model is a useful tool in visualising solutions, but the key input is engagement of key stakeholders at critical design stages. Here again, technology can play a part; Parsons Brinckerhoff has equipped rooms as ‘Design Caves’ and the use of a wall-sized smartboard is now a normal feature of the design review culture. The smartboard allows interactive viewing and manipulation of the 3D model by the whole team and mark- ups of key points and issues on-screen.

Previous experience on large multi-disciplinary projects has already embedded some necessary cultural behaviours within Parsons Brinckerhoff. In particular, many projects have been completed working with drawing and 2D model files within a document management system. This enables information sharing across disciplines, the ability to include references produced by other disciplines (to provide a complete set of information on a drawing) and ownership of the design by the relevant discipline. Parsons Brinckerhoff is also a fully multi-disciplinary company and has a strong existing culture of cross-discipline collaboration.

While BIM builds on these methods, a significant change in design culture for the BIM approach employed on a project has been the transition to working directly with the 3D model. Previous practice in bridge design, for example, had been to commence with 2D plans, sections and elevations, and develop a 3D model, if required, based on these. The BIM way of working has required new modelling skills to be learnt – to work directly with the 3D model and produce all the drawings from the model.

Model refinement and level of detail

Care is needed with communicating the degree of refinement of the model and the level of detail it contains. A significant culture change is required to realise that a 3D model is not necessarily any more accurate or detailed than a 2D equivalent, and indeed can even contain a range of refinements within the same model.

Early conceptual design work is often carried out using Ordnance Survey mapping data, due to the unavailability of detailed survey data. Whilst the mapping data has well-understood limits of accuracy, it is still capable of surprise when, for example, an offset of around a metre between point cloud survey data overlaid with an earlier 3D representation derived from OS mapping is evidenced.

A further example of this is the simplification to horizontal platform surfaces at early design stages to minimise modelling effort during development of alternative designs, but recognising that, in due course, the true vertical alignment of the platform will need to be incorporated.

fig 14 Water Street point cloud

It is therefore essential to understand and communicate what the model represents. This issue of reliability of modelled data can be managed through level of detail (LOD) schedules and layer-naming conventions. Visual techniques and symbology borrowed from architectural practice are also successful, for example using transparency or clearly ‘blocky’ models to represent lower levels of design refinement, or using false colours.

Simplicity in complexity

One of the challenges of BIM is the sheer volume of information that can be contained in the common data environment. Ultimately, this digital data needs to be understood by people – so simplicity and clarity are paramount. In this context, 2D representations still have a useful role alongside the 3D model. The advantage of the traditional drawing format is that it focuses attention on a selected sub-set of information, typically including critical interfaces. Indeed, the procedural task of arranging and marking up a drawing is often a key step in the thought-process of the designer, since it forces a rationalisation and communication of the important aspects of the design.

Drawings traditionally contain their own ‘metadata’ about the design including, among other things, the basis of the design, such as input survey information, specification notes and residual risk information to satisfy a designer’s responsibilities under CDM. Drawings undergo well established checking procedures, invariably involving coloured pens, to give assurance of a quality output.

At present, Network Rail’s engineering assurance procedures require submission of 2D drawings to their prescribed CAD standards. These procedures and standards have been developed over many years to minimise the risk to the operational rail network of works to the infrastructure. There remains a challenge to determine how best the 3D model can operate in conjunction with formal review procedures.

Parsons Brinckerhoff has used techniques to produce 2D drawings based directly on information extracted from the model. Review of these drawings, using traditional methods, combined with the involvement of the responsible engineer in the modelling process, provides confidence in the model necessary to allow each discipline’s input to the model to be ‘approved’.

Moving up the wedge

Parsons Brinckerhoff takes care to employ a range of digital tools and software appropriate to the design stage.

Although there are sophisticated, discipline-specific BIM modelling tools available, particularly at early design stages a simpler approach can focus attention better on key design issues.

This approach allows a design team to focus on the challenges of coordinating a large, complex design concept between multiple disciplines. It is often the case with rail design that the optimum solution is only achieved after several carefully-considered iterations. Software tools aimed at streamlining the design process with built-in ‘auto-generate’ functions are not always appropriate in this situation.

A further advantage consideration is the size of the model files. Technology moves on, but even so there remains a need to avoid placing excessively heavy demands on the hardware and allowing reliable manipulation of the geographically large models. For example, a client and its design team must be able to hold day- long coordination sessions, regularly flicking between 2D and 3D views of a model, without the screen freezing or interrupting the flow of discussion.

Different geometries, different solutions

The application of BIM to projects within the building sector has been common for nearly a decade. This position is supported by the availability of effective software that provides much of the functionality to support the BIM process.

In contrast, the use of BIM on infrastructure projects is less widespread. This is due, in no small part, to the differences in geometry involved and the types of software which can deal with these.

The contrasts between applying BIM to different sectors are illustrated by a crude classification into different geometries. Buildings generally take a vertical form of construction; horizontal floor plates are stacked vertically and the interfaces tend to be internal rather than external.

In contrast, infrastructure projects tend to take a horizontal form. Transportation projects typically extend along a linear corridor governed by cross-sectional and alignment rules. Other forms of infrastructure project such as energy installations could be considered as surface-based.

This distinction is useful since techniques, modelling tools and data schemas may not be equally effective across different forms of geometry. Thus, a modelling tool that can readily generate repetitious floor plates may not be the most suitable for a linear project. These considerations can assist the expert practitioner – the designer – to select the most appropriate digital toolset for the job. This recognises that different tools may be needed among and even within sectors.

fig 10 vertical piccadilly

Rail projects can be challenging since they combine features of these different geometries. The rail environment itself is linear but also intersects other linear features at different levels including roads and rivers, and includes vertical construction at the stations. At key locations such as elevated stations, there can be four or more levels to coordinate: utilities and watercourse culverts below ground; highways, urban realm and substructure at street level; railway and platforms on a viaduct; pedestrian footbridges providing platform access; station roof-space and building services above.

Additionally, there is a difference in scale between building and infrastructure projects. Track models may include whole sections of route covering many kilometres, and these may need to be broken down into sections of 1.0km to 1.5km of track length. Surrounding buildings and streets may be modelled to provide context and illustrate the relationship between the new works and the urban realm. In this respect, the BIM process can generate some additional workload over and above what would normally be required in 2D, where a simple overlay on an Ordnance Survey tile would suffice. However, this can provide the key benefit of enabling easy understanding and visualisation of the proposals.


BIM, particularly for infrastructure projects, is difficult to define precisely; Parsons Brinckerhoff has instead focused on the outcomes required from BIM and acknowledged that different sectors may approach BIM from different angles. The challenge that BIM addresses is the fragmented and inefficient manner in which digital data is used in the construction industry. Tackling this has and will require innovation, the use of appropriate digital tools and a huge cultural change, building on existing design processes.

The successful implementation of BIM methods and processes can deliver benefits in producing efficient, coordinated designs; allowing clear presentation of complex interfaces to a variety of stakeholders, while reducing trackside safety risks during the design period. BIM has been used as a tool to bring diverse technical disciplines together in a common understanding at the early, critical stages of design, requiring technological investment but also cultural changes.

One of the challenges for implementing BIM for infrastructure projects in the UK is to look forwards as well as backwards, making best use of the latest tools available without erasing the legacy from previous generations. Using the same yardstick, perhaps the challenge for a successful application of BIM is to ensure that our twenty-first century models prove useful to our successors in the twenty-third century.