Fouling Point Marking

[Dungrange]

Although not applying to main line railways, the army guide, Depot Layouts, Reconnaissance and Planning 1943, defines the fouling point as follows.

 

Fouling point - limit of wagon standing to be taken as 11 ft. 2 in. centres.

 

I make this a fraction under 45 mm.

 

This is the bit that I don't quite understand, insofar as standard track centres for a double track line are 11' 2" centres.  Therefore taking this definition, the fouling point of a crossover between the up and down lines would be the tips of the point blades.  However, in signalling there seems to be a difference between the fouling point and the clearance point, with the clearance point being, I think, generally 16' 6" from the fouling point.  My understanding of this is that providing the leading axle of a locomotive is clear of the clearance point, it will not foul the adjacent line.  When operating Track Circuit Block, I think the Clearance Points define the change points between adjacent track circuits. However, if we were to assume that the fouling point is at the tips of the point blades of a crossover, then the track circuit joints would be 16' 6" from the tips of the point blades, but the standard lead on a turnout is much less than this.

 

I'm therefore tempted to assume that the Clearance Point would be the rail joint at the toe end of the turnout that forms a crossover and as such, the distance at the fouling point would be less than 11' 2".

 

I guess the follow on question that relates back to the original post is does a fouling point marker actually indicate the fouling point or the the clearance point and is a consistent definition used in all departments (eg both signalling and operations).

[Penlan]

..... Fouling point - limit of wagon standing to be taken as 11 ft. 2 in. centres.

I make this a fraction under 45 mm.

 

I think possibly 3.15 metres might be nearer the mark, unless I'm missing something - Oh, unless you mean roughly in 4mm scale.

[sigtech]

Applying this principle to 'Sproston' my 00 gauge layout, fouling points for the goods yard sidings are marked visually by using offcuts of code 100 rail, about 1"" long, painted white and mounted vertically in a hole drilled in the board at the convergence of the tracks. It also serves to indicate where some of the underboard magnets are situated for uncoupling.

 

Regards,

SIGTECH

(Steve).

[TheSignalEngineer]

This is the bit that I don't quite understand, insofar as standard track centres for a double track line are 11' 2" centres.  Therefore taking this definition, the fouling point of a crossover between the up and down lines would be the tips of the point blades.  However, in signalling there seems to be a difference between the fouling point and the clearance point, with the clearance point being, I think, generally 16' 6" from the fouling point.  My understanding of this is that providing the leading axle of a locomotive is clear of the clearance point, it will not foul the adjacent line.  When operating Track Circuit Block, I think the Clearance Points define the change points between adjacent track circuits. However, if we were to assume that the fouling point is at the tips of the point blades of a crossover, then the track circuit joints would be 16' 6" from the tips of the point blades, but the standard lead on a turnout is much less than this.

 

I'm therefore tempted to assume that the Clearance Point would be the rail joint at the toe end of the turnout that forms a crossover and as such, the distance at the fouling point would be less than 11' 2".

 

I guess the follow on question that relates back to the original post is does a fouling point marker actually indicate the fouling point or the the clearance point and is a consistent definition used in all departments (eg both signalling and operations).

Fouling points and clearance points as far as track circuits are concerned were defined in this document. https://www.rssb.co.uk/rgs/standards/SSP036%20Iss%201.pdf

[TonyA]

 

..... Fouling point - limit of wagon standing to be taken as 11 ft. 2 in. centres.

I make this a fraction under 45 mm.

 

I think possibly 3.15 metres might be nearer the mark, unless I'm missing something - Oh, unless you mean roughly in 4mm scale.

 

 

Sorry. I did mean in 4 mm in all it's forms!

 

Neither the army manuals nor my course notes from Longmoor actually define "fouling point". However it is used to define the usable length of a siding where track centres would normally be wider than on a double track running line.

 

You also have to remember that the army has its own name for things. That is why a wagon for carrying liquids is a cistern wagon while a tank wagon carries tanks. 

 

Tony

[Dungrange]

Fouling points and clearance points as far as track circuits are concerned were defined in this document. https://www.rssb.co.uk/rgs/standards/SSP036%20Iss%201.pdf

 

Thanks - that document seems to define the fouling point as being when the distance between the outside faces of the rail are 6', which is of course consistent with the fouling point being defined as when track centres reduce below 11' 2".  On that basis, the fouling point of a crossover would appear to be the tips of the switchblades.

 

A similar RSSB document (https://www.rssb.co.uk/rgs/standards/RIS-0728-CCS%20Iss%201.PDF) provides a slightly different definition from the inside faces of the rail, but seems to end up with effectively the same answer.

[TheSignalEngineer]

Yes, I think that's the latest version. It's more or less as I remember what was in the Signalling Design documents many years ago when I was involved in that sort of thing.

[The Johnster]

I would say that, for modelling purposes, the fouling point is where vehicles are able to contact each other and will depend on the largest/widest/longest vehicles using the line with regard to overhang on curves.  A way of dealing with this while the layout is under construction and at the stage where track is laid but no scenery has yet appeared is to take your longest and widest vehicle, usually a coach. and tape different colour felt tip pens to it a the centre or each side and the corners at each end, colour coded to represent their positions on the coach.  Each pen has it's tip touching the baseboard.  

 

Now, gently push the coach around the entire layout with a slight downward pressure, lifting the pens over pointwork etc.  You will at the end of the exercise have a set of 3 slightly wobbly but fairly continuous coloured lines at the side of each track.  Where these lines intersect at junctions are your fouling points; if they intersect anywhere but at a junction you need to relay your track or you will have a clearance issue.  You will have spotted that in fact this is inaccurate to the extent of half the diameter of the pen, which is enough for clearance and provides a safety margin at the fouling points.

 

This is how real railways do it, haven't you seen those trains running late at night when nobody is about with the massive felt tip pens bolted to the sides and ends?  (I may have dreamed this).

 

You need to know the fouling points in order to position your signals, and to determine the capacity of your sidings.  If you are using setrack geometry then you can safely regard the fouling point as the rail join of the point, but the end of the vehicle must not be left over that and you cannot get away with taking the leading wheel up to the join.  For realism, leave even more room than that if you can; on the real railway fouling points are rarely approached to within less than a wagon length, especially in yards and sidings where staff may be riding on the steps of shunting locos in the course of their duties (you will find plenty of examples that contradict this statement, but by and large it is better not to make your model look overcrowded).  Similarly, signals are close to but not on top of fouling or clearance points, and trains do not stop actually at them but a few feet, or sometimes yards, short; this is so that the driver can see the signal from his seat without craning his neck.

[Dungrange]

I agree with you about the need not to make the model look crowded.  There's nothing worse that seeing one item of rolling stock pass within millimetres of another when in the real world there would be a few feet or even a few wagon lengths between. However, as railway modellers, we are often cramped for space and apply selective compression to fit things in.  This means that there is often a need to ignore what the real railway may try to do (when it has the space available) and instead focus on what the real railway does when it has similarly constrained conditions (for whatever reason).

 

In my particular instance I have a crossover in the station throat at the end of the platforms.  There is therefore a fouling point (where stock could physically touch).  I understand that the clearance point should be 4.88m (around 16') from the fouling point. The insulated rail joint for the track circuit boundary for the colour light signalling would be at the clearance point (to indicate that any unit is definitely clear of the fouling point).  The insulated rail joint at the track circuit boundary would also be the replacement IRJ for the starting signal, which would usually be 5 m in advance of the IRJ.  Then, as indicated there needs to be some space between the front of the unit and the signal so that the driver can actually see the signal - I think a minimum of around 6' (2 m) is desirable on the prototype.  Unfortunately all of these little distances add up.  Fouling point to clearance point - 64 mm (in 4mm scale). Clearance point to signal - 65 mm (in 4mm scale).  Signal to front of unit in platform - 24 mm (in 4 mm scale).  This therefore means that the front of my unit sitting at the platform should be at least 153 mm (6") from the fouling point.  At the other end, there also needs to be space between the unit and the buffer stop (again, I think a unit is supposed to stop 2 m from the buffer stop).  Therefore fitting the desired train length into the planned platform length and providing all of these clearances may be a challenge, hence my reason for trying to accurately determine where the fouling point (from which the clearance point is measured) is in the right place.

 

If I measure my 153 mm from the tips of the switchblades, I will clearly have a lesser usable platform length than I will if I measure from the point at which two vehicle will actually come into contact.

[The Johnster]

There is, I think, a need to establish early on and in the planning stage of a model railway what the maximum length of trains is to be and how they are going to be worked.  My rule of thumb is that, having established the maximum train length, the platform should be at least a coach length longer, and that clearing points are beyond the platform ends.  By and large, a layout should be at least 3x the length of the longest possible train (IMHO; there are other HOs available), a length for the platform, one for the station throat, and one for the fiddle yard.  This ratio goes to 4x in the case of a through station because there is another station throat.  If the layout can be lengthened beyond this it is better to do this than to increase the train length and upset the proportions, if you can...

 

Some of these dimensions are a bit frightening in the limited space most of us have to contend with, but I have found these proportions to have served me well over many years and commend them to your consideration.

[Dungrange]

To a certain extent, I am still at the planning stage albeit the baseboard on which the station throat sits is under construction and is all drawn up in Templot ready for track building.  My desired maximum train length is a Class 221 5-car Voyager unit (5') although the majority of passenger services will comprise a mix of 2 x Class 158 Units (4') and Class 170 units (3').  At approximately 3' 3", my station throat will not meet your target of one train length (ie the rear of a Class 221 set will still be in the platform when it disappears into the fiddle yard), but I can live with that.  One day, I may build an extra board to fit between the layout and the fiddle yard - but not this decade.

 

If I define the Clearance Point as being either the tips of the switchblades or the rail joint at the toe end of the crossover, then this is beyond the section where the platform is level (but within the sloping section).  However, if I take the Fouling Point to be the tips of the switchblades (ie where the distance between tracks starts to reduce below 11' 2" track centres), and then measure back 16' (4.88 m) to define a Clearance Point, then this does lie within the section where the platform will be full height and therefore restricts usage of what I thought would be a platform that could accommodate a 5-car unit.

 

Conversely, the actual Fouling Point, as defined where two vehicles just touch (using the felt tip pen method), is some 75 mm (3") beyond the tips of the switchblades (principally because the crossover is a pair of B8 turnouts with a total length of approximately 580 mm - I'm not using Setrack geometry).  Ideally, I don't want the front of my 5-car set to be beyond the switchblades of the crossover, but need to be able to get the front of the unit sitting as close to that point as possible.

[dunnyrail]

I have always pondered this issue in UK. The examples shown appear to be local initiatives probably by wily Managers after some nasty experiences. Works OK with Local Bods that know the score, but for irregular Drivers. Hmmm memory. I do in fact find it surprising that a system was never implemented in UK. On the many NG Lines in Europe and Main Lines too a simple setup of a Red or Red and White marker is placed at the point where one train is on the verge of giving another a Sideswipe if both trains passed the marker point. Simples, I model these on my G Scale Harz System for two reasons. A - because thay are on the prototype. B - it helps my irregular Operators define correctly stopping points. G scale Trains are big and expensive, I do not want them damaged unecessarily. Now while there is possibly no apparent practice for Steam Age British Railways I can see no reason why a small peg made out of a Matchstick and painted Red or White should not be placed in tne appropriate place. On exhibition layouts it would certainly be a talking point!

JonD