RAD — Railway Alignment Designer Open the designer Open the designer

Reference

The engineering behind the tool, and how to drive it.

Why the curve has a curve at each end

A train entering a circular curve from a straight would meet full centrifugal force instantly. So the two are joined by a transition whose curvature grows steadily from nothing to 1/R. The curve that does this is the clothoid, or Euler spiral:

1/r(l) = l / A²    where A² = R · Ls
θ(l) = l² / (2A²)
x(l) = ∫ cos θ ds    y(l) = ∫ sin θ ds

Cant is raised along that same length, at a constant rate. Because curvature and cant rise together, the resultant force stays in the plane of the track the whole way through. That is the entire reason the clothoid is the right shape.

Fitting one at an intersection needs two derived numbers. The spiral pushes the circular arc away from the tangent by the shift p, and the spiral begins k back from the foot of the perpendicular from the arc centre. Standing the centre off (R+p₁) from one tangent and (R+p₂) from the other and solving gives the tangent lengths:

T₁ = k₁ + [ (R+p₂) − (R+p₁)·cos Δ ] / sin Δ
T₂ = k₂ + [ (R+p₁) − (R+p₂)·cos Δ ] / sin Δ

With equal spirals this reduces to the familiar T = k + (R+p)·tan(Δ/2), and with no spiral at all to R·tan(Δ/2). Asymmetric transitions are not a special case — they fall out of the same expression.

The tangent points are named the usual way: TS tangent to spiral, SC spiral to circular, CS circular to spiral, ST spiral to tangent. Without transitions they become TC and CT.

Cant, deficiency and excess

Equilibrium cant balances the centrifugal force exactly, at one speed:

C = G · V² / (127 · R)    [mm], V in km/h, R in m, G in mm

G is the dynamic gauge — the distance between rail centres. With G = 1750 mm this is the Indian Railways form C = 13.76 V²/R; with 1500 mm the standard-gauge C = 11.81 V²/R. One equation, every gauge.

Real track carries trains at different speeds, and only one cant can be built. The fast train is left short by the cant deficiency, the slow one over-canted by the cant excess. So a cant exists at all only when

C_eq(V) − Cd_max  ≤  C_eq(V_slow) + Ce_max

Rearranged, that sets a minimum radius for mixed traffic which is separate from, and often larger than, the one the fast train alone implies:

R ≥ G (V² − V_slow²) / (127 (Cd_max + Ce_max))

Below it no applied cant satisfies both trains, however you choose it. The tool reports this as R_MIXED, and it is the reason it will sometimes insist on easing a radius rather than adjusting cant.

How long the transition has to be

Three independent criteria; the longest wins.

rate of change of cant      L = C · V / (3.6 · limit)
rate of change of deficiency  L = Cd · V / (3.6 · limit)
cant ramp gradient            L = C · N / 1000   (1 in N)

Each curve card names which one governed, so you can see what to relax if the transition is longer than the site allows.

The compliance codes

Errors break the standard's exceptional limit. Warnings sit between the normal and exceptional limits, or flag desirable practice. Every finding names the rule it comes from, the clause behind it and the ways out, under Why?. Most also have a Fix button; the ones that would need the route, the speed or the works changed are advisory, and say so rather than guessing on your behalf.

The report groups by the part of the design a finding belongs to, and the filter box takes a code, a chainage or a word from the message. Strict reports every warning as an error. The ⊘ button on a finding turns that rule off for the project — recorded in the project file, and listed above the report, because a check that has quietly stopped running is worse than one that fails.

Horizontal

R_MIN, R_ABS radius below the minimum for the speed or the gauge · R_MIXED no cant serves both speeds · CANT_MAX, CD_MAX, CE_MAX cant, deficiency or excess over the limit · ARC_SHORT too little circular arc

Transitions

NO_TRANS cant with no transition to run it in · LS_SHORT shorter than required · DCANT_DT, DCD_DT cant or deficiency changing too fast · CANT_GRAD ramp too steep

Between curves

IP_OVERLAP, OVERLAP curves running into each other · NO_STRAIGHT, STRAIGHT_SHORT too little straight between them · REVERSE_OK a reverse curve whose transitions meet cleanly

Vertical

NO_VCURVE a grade change with no curve · RV_MIN vertical radius too small · AV_MAX vertical acceleration over the limit even where the radius passes · VC_SHORT a vertical curve too short to set out · V_OVERLAP vertical curves colliding

Gradients

GRADE_MAX over the ruling gradient · GRADE_COMP over it once compensated for curve resistance · GRADE_SHORT a gradient too short to run a train over without surging · V_ON_TRANS a vertical curve twisting the track where cant is already changing

Curvature steps

R_RATIO compound curves whose radii are too far apart · VIRT_TRANS a curve entered with no transition, where the deficiency has to build over the vehicle's bogie centres instead of a designed length

Terrain and works

Only when a ground profile is loaded. CUT_DEEP, FILL_HIGH a tunnel or viaduct far past the depth at which it became worth building · STRUCT_ON_TRANS a deck or bore spanning a transition, so it has to be built to a twisting surface · TUNNEL_DRAIN a bore too flat to drain · EARTH_BALANCE cut and fill badly out of balance

The engine itself

RULE_ERROR — a group of checks failed to run. The rest of the report still stands, and this says which part of it is missing rather than going quietly blank.

Laying out a route

Design a route opens on the whole country and takes an ordered chain of points. A and B are the two ends. Everything between them — C, D, E — is obligatory: the router is free within a leg and pinned at every one of them. That is the difference between a corridor a cost function happened to like and one that meets the junction, uses the gap and serves the town, which is what a railway is actually routed on.

Three ways to place a point

Click the map, type a coordinate — 27.175, 78.042 or 27 10 30 N, 78 02 31 E — or search a place, a station name or a station code. Codes are what no geocoder indexes and what every railway person has to hand, so AGC and NDLS are looked up as OpenStreetMap tags directly.

Moving them

Every pin drags. Click the corridor between two pins to add an obligatory point on that leg, or use ＋ Intermediate point and then click. Right-click a pin to remove it. A pin dragged away from the station it was found under loses that name, because it is no longer that station.

What survives

The grid path is thinned into an IP polyline, and thinning is exactly the step that could slide the route past a point you pinned. It does not: where an optional vertex crowds an obligatory one, the optional one goes, and the result names the IPs that were held.

Speeds

Design speed sets the curves; slowest traffic sets cant excess, since cant chosen for 160 km/h is cant a goods train rides on its inner rail. Slow traffic is capped at line speed, because above it, it is not slow traffic.

A line that is already there

Before any geometry is designed the corridor is checked for a railway already joining the two stations. Where there is one the run stops and says an existing connection exists, counts the running lines it has, measures whether its curvature will hold your design speed, and offers to design a doubling, a 3rd line or a 4th line beside it instead of a new corridor — parallel where the old alignment complies and on new geometry where it does not. It proposes; you decide.

Terrain detail is yours

The button picks the ground grid the design is built on — 200, 120, 60 or 30 m — and that is exactly what you get. Under it, what the setting costs for this corridor: tiles, memory and roughly how long. The setting that gives the best detail the corridor carries comfortably is ringed. It is a suggestion, not a decision: pick a finer one and it tells you the price and runs it anyway. A 150 m nala reads anywhere between 2 m and 15 m deep on a 200 m grid depending where it falls between nodes, and the bridge opening follows that — so on broken ground, finer is worth the wait.

What it cannot know

Whether a corridor needs another line is a traffic question, and the traffic is not in a map. Nor is which side of the existing formation the land is available on — that is scored against water and built-up ground and offered as a default, to be overridden in Design considerations → Inclusion.

Basemaps and georeferencing

The plan view can draw a street map, satellite imagery, topography or shaded relief under the alignment, so a curve can be moved against the ground it actually crosses rather than against an empty grid. Shift+F, or the ⤢ button, gives the plan the whole window for that work.

Where it comes from

A route designed with Design a route already knows where it is. An alignment drawn by hand needs one point tied to the earth: pick the point in the Plan tab and give its latitude and longitude, in decimal degrees or as 27 10 30 N, 78 02 31 E. It is saved with the project.

What it assumes

The plane is treated as a project grid — a transverse Mercator on that longitude, north up, scale 1. The panel reports how far grid distance drifts from ground distance at the point you tied down, in parts per million, so the assumption is visible rather than silent.

Accuracy

Tiles are placed by reprojecting each one's own corners, not by stretching the whole image, so the imagery stays registered to the alignment at any zoom. Basemaps are for context and judgement, not for setting out.

What comes out, in detail

The landing page lists the formats. This is what is inside them.

5 km Plan & Profile sheet packages (.dxf & viewer)

Production-standard Final Location Survey drawing sheets, partitioning any corridor length into 5 km packages. Each carries an upper plan strip with track, land boundaries tagged at 25 m, boxed kilometre posts, curve data apex boxes and bridges; a lower seven-row L-Section data grid — formation, ground, cut/fill, alignment, gradients — with exact chainage vertical callouts; an independent 10 m datum per sheet at 1:25000 horizontal and 1:500 vertical; and a title block carrying project title, division, sheet number and km range. Everything sits on named CAD layers. Viewable on screen with zoom, pan and sheet paging before export.

Station yard conceptual plans (.dxf)

Main running lines, passenger loops, goods sidings and shunting necks; island and side platforms with standard clearance envelopes; 1 in 8.5 and 1 in 12 turnouts with fouling markers; 800 m clear standing length loops; 6.10 m track centres for BG running loop clearance. Vertical plateaus at a maximum 1 in 400 (0.25%) are inserted automatically so a yard never lands on a steep grade, which is what the Indian Railways Schedule of Dimensions requires.

Multi-sheet Excel workbook (.xlsx)

Cover, setting-out table, horizontal curves, vertical curves, civil structures, a cut and fill report with mass-haul balance, land acquisition pegs, and the compliance report — one workbook.

Google Earth 3D model (.kml / .kmz)

Terrain-clamped centreline, a 3D rail elevation ribbon, boxed kilometre posts and station yard footprints, for walkthroughs and stakeholder presentations.

LandXML 1.2 alignment model

Clothoid spirals, circular curves, tangents and vertical grade lines in standard LandXML — read directly by Autodesk Civil 3D, Bentley OpenRail and 12d Model.

Hydrology & crossing schedules (CSV)

Catchment areas in km² from 2D D8 flow accumulation over the DEM, Dickens and Lacey waterway opening dimensions, and consolidated road over/under bridge schedules after minor roads have been rationalised into grade-separated crossings.

What it is not

This matters more than the feature list. The tool produces an accurate, standards-compliant first pass and preliminary design. It is an engineering accelerator, not a replacement for field verification.

Keyboard

Editing

F zoom to extents · Tab / Shift+Tab next or previous point · Delete remove the selected IP · ↑ ↓ in a numeric cell steps the value, with Shift for ten steps

Files

Ctrl/Cmd+Z undo · Ctrl/Cmd+Shift+Z redo · Ctrl/Cmd+S save · Ctrl/Cmd+O open

Account

Optional, and it buys the project library — projects kept across machines with a revision behind every save. Sign in with a password or with a link by email, from the button at the right of the toolbar, where your picture appears once you are in. Files on disk work exactly the same either way.

Views

Wheel zooms · drag pans · drag a point in the plan or a VIP in the profile to reshape, with Shift in the profile holding the chainage · Shift+F puts the plan full screen, Esc leaves it · Shift+wheel in the profile changes the vertical exaggeration · double-click empty space in the plan inserts an IP · [, or the button at the end of the tab strip, folds the side panel down to its icons and gives the width to the views; any icon opens it again on that table

Drawing overlay tools

Beyond the computed alignment, the plan takes manual drafting for constraints and context. Shapes live on layers with specific semantic meaning, rather than just being lines on a screen.

The shape types

The overlay handles basic geometry: line, rect, polygons, note markers, dimension (dim) lines, and deadend buffers. They are drawn in map space, so they move with the terrain, not the viewport.

Context layers

notes, sketch, and measure are for visual markup. trace holds reference lines you want to follow. trackwork and existing denote permanent way that is already on the ground, serving as visual constraints when weaving a new alignment.

Router constraints

The avoid and include layers change how the autorouter behaves. An avoidance polygon creates a hard penalty wall the router will not cross, forcing it around protected land or built structures. An inclusion polygon is the inverse: it forces the generated corridor to pass strictly within its boundary, ensuring the route serves a specific land parcel or corridor.

Station yard design

Yards are laid out as conceptual plans directly on the alignment, carrying standard clearance and operating geometry without needing a separate CAD session.

The yard editor workflow

Pick a station and the editor sets out main running lines, passenger loops, goods sidings, and shunting necks. You choose the platform arrangement — island or side — and it enforces standard clearances, such as 6.10 m track centres for BG running loops and 800 m clear standing lengths.

Turnouts and fouling

The editor models standard 1 in 8.5 and 1 in 12 turnouts. It automatically computes and places fouling markers where converging tracks drop below safe clearance, ensuring the declared standing length is genuinely available for rolling stock.

Plateau grading

A yard cannot sit on a steep gradient. The vertical alignment is automatically checked and flattened into a yard plateau at a maximum of 1 in 400 (0.25%), inserting vertical curves to tie it back to the ruling grade, meeting the Schedule of Dimensions requirement.

Export

The finalised layout drops straight into the DXF export, meaning the 5 km sheet packages carry the fully modelled station limits on standard CAD layers, not just a centreline.

Multiple tracking

When adding lines to a route that is already there, the geometry depends on whether the old line is fit for the new traffic.

Existing line detection

The router checks the corridor for a railway already joining the stations. If it finds one, it measures how many running lines exist and offers to design a doubling, 3rd line, or 4th line.

Speed compliance and realignment

A parallel offset is only drawn where the existing curvature supports the new design speed. Where a curve is too tight, the tool drops the parallel offset and designs a realignment — new geometry on a wider sweep that complies with the standards.

Tie-in points

Where a realignment separates from the old line and where it returns, the tool automatically calculates the tie-in points. This ensures the new track smoothly rejoins the existing formation, keeping land acquisition and earthwork for the deviation to a minimum.

Cost estimation

The estimate is built from the geometry, structured exactly as Indian Railways expects to read it.

IR Finance Code plan heads

Costs are grouped into the standard General Abstract structure — Civil Engineering, General Charges, Contingencies — split into Cash and Stores columns, with departmental levies cascading down to the final total. It is formatted to drop straight into a sanctioned estimate sheet.

Deriving quantities

Earthwork is derived from average end-area over a trapezoidal formation, cut from the terrain grid. Formation works follow the length. Crossings are priced by sizing the required structure: minor bridges take their span from the calculated catchment hydrology, while road conflicts dictate over- or under-bridges based on grade separation levels.

What is withheld

If waterways are unsized, conflicts are unresolved, or the corridor hasn't been looked up, the total is deliberately withheld. A cheap total missing all its bridges is worse than no total. The tool lists the missing decisions instead of showing a false number.

Where the numbers come from