I want to set up the platform at the passenger halt to be "to scale" for both 00 and H0 trains. This is possible for a straight track, as long as the 00 models are to scale width (or narrower), and any H0 models, where outside cylinders usually protrude too far, are less than 35 mm wide. These are the allowable dimensions:
- Height of platform surface above rails: 12.7 to 13.0 mm (I'll call this half an inch)
- Offset of platform edge from track centre line: 19.0 mm (I'll set this up with my broadest vehicle)
- Width 33 mm or greater
Here are the calculations to show how I have come to these figures.
The maximum allowed stepping distances for British railways are defined in Railway Group Standard GM/RT2149, these are 275 mm horizontally and 250 mm vertically. These are the biggest gaps the railway expects its passengers to negotiate. The smallest gap between the underside of a step and the top of a platform is typically 50 mm, and for my model platform, I'll aim for 1 mm.
I shall use my Hornby 00 Mk3 coach for the basic dimensions.
The maximum width of a British outline train below platform height is 8 ft 8 in, which equates to 34.8 mm for a scale model in 00. For H0, outside cylinders are usually over the scale width, but modern models are usually narrower than similar 00 ones.
The space available for a station platform in Britain is defined in Railway Group Standard GIRT7073. Figure A.1 of Issue 2 (June 2018) shows a space up to 915 mm above rail level, plus an extra 10 mm for maintenance and installation tolerances. In the past, station platforms were often lower, and for this blog post the model platform height is a derived dimension not a constraint. The objective is to make the model look right so I will ignore the scale equivalents of the platform height.
The foot board on the Hornby 00 Mk3 coach is 16 mm above rail level, representing 4 feet. The 00 scale equivalent of 250 mm is 3.3 mm, and so the lowest representative height of a model platform is 16 - 3.3 = 12.7 mm.
The foot board on an equivalent H0 scale coach would be 14 mm above rail level. The highest platform I will accept here, with my nominal 1 mm minimum clearance is 14 - 1 = 13 mm.
The acceptable vertical dimensions for 00 and H0 are indistinguishable to a viewer.
The width across the foot boards on the Hornby coach is 36 mm. These foot boards taper (like the real thing), so this measurement is at their narrowest point. This 36 mm represents an offset of 18 mm from the outer edge to the centre line of the track for 00 gauge. The smallest distance I will accept for 00 is 18 + 1 = 19 mm.
The width across the foot boards on an equivalent H0 scale coach would be 31.5 mm, giving an offset of 15.8 mm from the centre line of the same track. The H0 scale equivalent of 275 mm is 3.2 mm, and so the largest representative distance of the platform edge from the track centre line is 15.8 + 3.2 = 19 mm.
The acceptable horizontal dimensions for 00 and H0 are identical.
Railway Group Standard GI/RT7016 gives the minimum unobstructed width of a platform as 2,500 mm. This distance is 33 mm for 00 gauge. The width of the model platform can be set to 33 mm, or the space available, whichever is the greater.
If the platform has relatively scale-free finishes, such as concrete, timber, stone blocks or gravel (but not brick or paving slabs), then one structure can suit both H0 and 00 trains, with the scale of the model set by the train in use.
Thank you to Clive Mortimore for posting the stepping distances of the full-size railway on the RMWeb.
Revised 9 Nov 2019