Table of Contents

Track spacing and structure limiting dimensions

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The following data on track spacing has been derived from Track Construction Without Tears, published by Slater’s Plastikard Ltd and is reproduced with their permission.

Space between adjacent tracks

(Usually measured between the outside edges of the rail heads).

Prototype Model Track Centres
mm imperial mm mm
Standard between a pair of main lines 1829 6ft 0in 42 77
Between a pair of main lines and one or a pair of additional running lines 3048 10ft 0in 70 105
Between a main line and siding 3048 10ft 0in 70 105
Between a main line and catch siding 1829 6ft 0in 42 77
Between goods yard sidings 1829 6ft 0in 42 77
Between goods yard sidings for carriageways 7315 24ft 0in 168 203
Between coal sidings 1829 6ft 0in 42 77
Between marshalling or sorting sidings 2134 7ft 0in 49 84
Between carriage sidings 2438 8ft 0in 56 91
Additional space to allow for lamp posts between sidings. etc. 610 to 1220 2ft 0in to 4ft 0in 14 to 28 91 to 105
Additional space to allow for large main line signal post 1372 to 1524 4ft 6in to 5ft 0in 32 to 35 109 to 112
Additional space to allow for ordinary main line signal post 1220 4ft 0in 28 105
Additional space for siding signal post 1118 3ft 8in 26 103

Note: The Guild Standard track centre distances are 80mm between main lines and 90mm between sidings. Additional spacing may be necessary on curves [link required]. The track centres shown in the table above include a 3mm allowance for the width of the rail-heads.

Clearance between tracks and structures

Prototype Model
mm imperial mm
Absolute minimum horizontal clearance to structures above platform height 1372 4ft 6in 32
As above. but desirable figure 1524 5ft 0in 35
Minimum clearance to structures in goods yards (e.g. shed doors) 1295 4ft 3in 30
As above, but desirable figure 1372 to 2134 4ft 6in to 7ft 0in 32 to 49
Absolute minimum vertical clearance on passenger lines 4420 14ft 6in 101
As above. but desirable figure 4572 15ft 0in 105
Absolute minimum vertical clearance in goods yards 4267 14ft 0in 98

Passenger platforms

Prototype Model
mm imperial mm
Height of platform above rail level 914 3ft 0in 21
Horizontal distance from outer edge of rail to extreme edge of platform coping 635 2ft 1in 15
Overhang of coping from wall face 305 1ft 0in 7
Minimum distance of pillars. etc. from edge of platform 1829 6ft 0in 42
Width of platform. small stations 1829 6ft 0in 42
Width of platform. large stations 3658 12ft 0in 84
Inclination of ramped ends 1 in 8 1 in 8

Goods and mineral loading stages

Height above rail of:

Prototype Model
mm imperial mm
Stage for (un)loading general goods 1067 3ft 6in 24
Cattle stage 1067 3ft 6in 24
Horse stage 1067 3ft 6in 24
Stage for loading high sided wagons with minerals, etc. by tipping 2438 to 2896 8ft 0in to 9ft 6in 56 to 66
Stage for coaling locos 1520 5ft 0in 35

Carriage loading docks

For loading a road vehicle onto a wagon, etc.

Prototype Model
mm imperial mm
Height above rail level 1220 4ft 0in 28

Water columns and cranes

Prototype Model
mm imperial mm
Space required when column is between tracks 3353 11ft 0in 77
Distance from rail to centre of column when column is outside tracks 1981 6ft 6in 47
Distance of column behind signal of line on which engjne takes water 18288 60ft 0in 420

Water troughs

Prototype Model
mm imperial mm
Height of rim above rail level 76 3 in 2
Height of water above rail level 51 2 in 1

Turntables

Prototype Model
mm imperial mm
Space between rim of turntable and an adjacent track 2743 9ft 0in 63

Engine pits

Prototype Model
mm imperial mm
Width between side walls 1143 3ft 9in 26
Depth of pit below rail level (inside) 660 to 737 2ft 2in to 2ft 5in 15 to 17
Depth of pit below rail level (outside;) 914 to 991 3ft 0in to 3ft 3in 21 to 23

Overbridges

Prototype Model
mm imperial mm
Minimum clear opening for single line 4166 13ft 8in 96
As above. but desirable figure 4724 15ft 6in 108
Minimum clear opening for double line 7569 24ft 10in 174
As above, but desirable figure 8077 26ft 6in 185
Minimum clear opening for four lines with one 10ft space 15596 51ft 2in 358
As above. but desirable figure with one 10ft 6in space 16307 53ft 6in 375
Minimum headway 4420 14ft 6in 101
Desirable headway 4572 15ft 0in 105
Width between parapets, turnpike road 10668 35ft 0in 245
Width between parapets, public carriage road 7620 25ft 0in 175
Width between parapets. private road 3658 12ft 0in 84
Height of parapets 1220 4ft 0in 28

Underbridges

Prototype Model
mm imperial mm
Headway - turnpike road 4377 16ft 0in 112
- public carriage road 4572 15ft 0in 105
- private road 4267 14ft 0in 98
Widths of roadways - as for overbridges
Height of parapets 1312 4ft 6in 32
Desirable width between parapets - single line 4724 15ft 6in 109
- double line 8077 26ft 6in 185

Buffer stop

Prototype Model
mm imperial mm
Length of buffer beam 2286 7ft 6in 53
Height of centre of beam above rail 1067 3ft 6in 25

Earthworks

Prototype Model
mm imperial mm
Width of cutting at 2ft below rail level for double track with 6ft space 9144 30ft 0in 210
Width of embankment at 2ft below rail level for double track with 6ft space 9144 30ft 0in 210
Inclination of slopes for ordinary ground 1.5:1 1.5:1

Ballast

Prototype Model
mm imperial mm
Bottom ballast, thickness 229 9in 5
Bottom ballast, width for single line 3353 11ft 0in 77
Top ballast, level of surface top of sleeper
Top ballast, distance of top edge from rail 991 3ft 3in 23
Maximum size of sieve 51 2in 1

Check rails on curves

According to the Board of Trade Rules, a check rail must be provided to the inside rail of the curve on curves of 10 chains (4620mm or 15ft 2in in 7mm scale) radius or less. This check rail is often slightly elevated above the running rails and made from 11ft 0in older second hand rail. Curves of greater than 10 chains radius are often checked if high speeds are required and, in certain other places be the track curved or straight, such as; on viaducts or bridges over a certain length and over paved level crossings (to both rails) etc.

Most model curves are sharper than 4620mm (15ft 2in) and are left unchecked. It is suggested that curves of less than 1m (40in) are fitted with check rails for appearance purposes.

Prototype construction gauge




The horizontal distances between prototype tracks and adjacent structures are increased for curved track to allow for the throw-over of long vehicles.

Radius of curve (m) All horizontal distances increased by (mm)
100 257
200 128
300 85
400 64
500 51
750 34
1000 26
1500 17
2000 13

Structure dimensions for O gauge



Figure 2

Originally published in the Gauge O Guild Manual. Adapted for the GOGWiki by Nick Baines.