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Railway Clearances by the Numbers
Keeping trains clear of structures and each other: outlines, curve throw, cant, the kinematic envelope, margins, track centres, refuges and infringements
Railway clearances with numbers: rolling stock outlines, centre and end throw, cant lean, the kinematic envelope, safety margins, track centres, refuges, infringements and out-of-gauge loads.
Start readingAbout this book
Every railway runs through a tunnel of empty space. A train needs room for its own outline, room to sway, lean and bounce as it moves, room for the track beneath it to be imperfect, and room on top of all that so that a small error does not become a collision. Structures beside and over the track, from bridge piers and signal masts to platforms, walls and loading chutes, must stay outside that space, and so must trains on the next track. Getting it wrong is expensive at best: a new overbridge that has to be rebuilt, a platform that strikes doors, a transformer that cannot pass a cutting. At worst it kills.
This book is for designers, project engineers and maintainers who place things near railway track, and for planners who move unusual loads along it. It assumes basic geometry and some engineering background. It explains, with numbers, how a clearance is built up from the vehicle outward: the vehicle’s outline, the extra width a curve produces at its middle and ends, the lean that cant gives it, the dynamic movements and track errors that make up the kinematic envelope, and the safety margin and service space beyond. It then covers track centres, refuges for people, infringements and how they are approved and recorded, out-of-gauge loads, and the clearance record.
The sources and their limits
The book draws on a set of Australian Rail Track Corporation engineering standards for New South Wales, carried over from the former Rail Infrastructure Corporation standards and issued between 2004 and 2007, and on Section 7 of ARTC’s Track and Civil Code of Practice for South Australia, Western Australia and Victoria, issued in 2007. Where a value from one of those documents is quoted, it is cited, and it is quoted for teaching: those issues may since have been revised or replaced. Real design must use the standard and corridor requirements that the rail infrastructure manager currently specifies for the line, and its approval.
The running case
This is an illustration. A civil engineering consultancy is designing a new road overbridge for a regional council where the road crosses a single standard gauge main line, on a 400 m radius curve with 60 mm of cant, close to a passing loop and a short industrial siding. Later the same corridor must carry an out-of-gauge transformer on a well wagon. The consultancy’s engineers must work out the clearances the bridge needs, check the track centres at the loop, provide for people at a long retaining wall, and plan the transformer move.
The consultancy, council, bridge, rolling stock and numbers are invented for teaching. They are not KEVOS® work.
How to use the book
Chapter 1 sets out the outlines and the vocabulary. Chapter 2 deals with rolling stock and load outlines, Chapter 3 with curve throw, and Chapter 4 with cant. Chapter 5 builds the kinematic envelope, Chapter 6 adds the margins and service space to reach the structure gauge, and Chapter 7 covers track centres. Chapter 8 deals with platforms, refuges and people, Chapter 9 with infringements and out-of-gauge loads, and Chapter 10 with surveys and the clearance record. Every chapter ends with an exercise and its worked answer.
Professional responsibility
This book is educational. Railway clearances are safety-critical. Design, construction near track, infringements and out-of-gauge moves are governed by the rail infrastructure manager’s current standards, corridor strategies and approvals, and by rail safety law, and they need qualified review. Nothing here replaces those.
An original treatment
The explanations, the consultancy case, the derivations, figures and exercises are original KEVOS® writing, built from geometry and mechanics. The ARTC documents are copyright; a small number of their values are quoted with citation for teaching, and none of their text, tables or drawings is reproduced.
Who this book is for
Civil and structural designers, rail project engineers, track and structures maintainers, and planners of out-of-gauge moves who need to understand how railway clearances are built up and checked.
What you will learn
- Explain the difference between a rolling stock outline, a kinematic envelope, a safety margin and a structure gauge.
- Calculate centre throw, end throw and cant lean for a vehicle on a curve.
- Build up a kinematic envelope point from track and vehicle tolerances and check its clearance to a structure.
- Check track centres, refuge provision and platform clearances against the governing standard.
- Classify and record infringements, and plan the clearance checks for an out-of-gauge load.
Inside this book
Chapters
- 01The space a train needsLearn the outlines that make up a railway clearance, from the vehicle's static outline through the kinematic envelope and safety margin to the structure gauge, and who is responsible for each.
- 02Rolling stock and load outlinesRead a rolling stock outline, compare the approved outlines from narrow to wide, see why a vehicle's length and bogie centres matter as much as its width, and check a load against its loading outline.
- 03Curves: centre throw and end throwDerive how far a vehicle's middle swings inside a curve and its ends swing outside, calculate centre and end throw for the running case, and see how throw changes near the ends of curves.
- 04Cant and the leaning vehicleCalculate how far cant tilts a vehicle towards the inside of a curve at each height, why the outer roof corner rises, how speed changes the lean on the springs, and what cant does under bridges.
- 05Building the kinematic envelopeStack cant, cant tolerance, track movement, wear and play, throw, body roll and bounce in order to find how far a moving vehicle can reach, and see which allowances dominate on a curve.
- 06Margins, service space and the structure gaugeAdd the safety margin and service space to the kinematic envelope, read lateral and vertical structure gauge dimensions, protect piers near the track, and set the running case's piers and deck.
- 07Track centres and adjacent trainsFind the distance two tracks must be apart for trains to pass with a safety margin, see why curves and differences in cant need wider centres, and manage tracks that are closer than the standard.
- 08Platforms, refuges and peopleProvide places of safety beside long walls with refuges, handrail devices or signs, size and space refuges, see why platforms are a deliberate infringement, and calculate a worker's warning distance.
- 09Infringements and out-of-gauge loadsClassify clearance infringements by how much margin remains, follow approval and register records, check an out-of-gauge transformer along its route, and use speed restriction to win back margin.
- 10Surveys and the clearance recordSurvey structures and track for clearance, check an as-built structure against its envelope, fix the track with datum markers, keep the register that catches change, and bring the book together.
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References and source notes
The manuscript and worked examples are original KEVOS® writing. References inform particular concepts; their authors do not endorse this book. Web references were consulted on 26 October 2026.
- Australian Rail Track Corporation, Engineering Standard NSW. BDS 11, Transit Space Standards (from RIC Standard C 2103) (2005). Source for the list of NSW rolling stock outlines, the vehicle and track effects assumed in deriving transit space, and the 200 mm safety clearance margin, quoted with citation in Chapters 2, 5 and 6. Issue 1, March 2005; check currency with ARTC before use.
- Australian Rail Track Corporation, Engineering Standard NSW. BDS 12, Structure Gauge 1994 (from RIC Standard C 2104) (2005). Source for the minimum lateral and vertical structure gauge dimensions, selected service dimensions and minimum track centres, quoted with citation in Chapters 6 and 7. Issue 1, March 2005; check currency with ARTC before use.
- Australian Rail Track Corporation, Engineering Standard NSW. BDS 13, Application of Kinematic Envelope (from RIC Standard C 2105) (2005). Source for the order of operations used to build a kinematic envelope and the centre throw relation, summarised in new words in Chapters 3 and 5. Issue 1, March 2005.
- Australian Rail Track Corporation, Engineering Standards NSW. BDS 14, Infringement of Transit Space Standards (from RIC Standard C 2106); BDS 17, Transit Space for Special Loads (from RIC Standard C 2109) (2005). Sources for the classification of infringements, the reduced margin at which operating action is required, the approval and register records, and the handling of special loads, summarised with citation in Chapter 9.
- Australian Rail Track Corporation, Engineering Standards NSW. BDS 09, Transit Space Policy (from RIC C 2101); BDS 18, Transit Space Handbook: Commentary (from RIC C 2110) (2005). Sources for the definitions of transit space terms, the maximum rail level allowance, and the history of NSW structure gauges and track centres, cited in Chapters 1, 6 and 7.
- Australian Rail Track Corporation, Engineering Standard NSW. BSS 01, Safety Refuges and Handrail Devices for Trackside Structures (from RIC Standard C 4010) (2005). Source for the clearance categories that call for refuges, handrail devices or signage beside long walls, and refuge spacing and size, quoted with citation in Chapter 8.
- Australian Rail Track Corporation. Track and Civil Code of Practice SA/WA & Vic, Infrastructure Guidelines, Section 7: Clearances (2007). Source for the clearance outlines used in that code, the treatment of exceedances and permanent infringements, the contingency gap at which approval and monitoring apply, and platform practice, cited in Chapters 1, 7 and 9. Issue 1.1, 1 August 2007.