Difference between a single line and a bi-directional line

[Ditop23]

Sorry if this sounds a daft question.

Is it correct, that you can go either way on a single line. ?

Thanks

 

[Haywain]

Sorry if this sounds a daft question.

Is it correct, that you can go either way on a single line. ?

Thanks

Normally, yes. In most cases you'd never get your trains back if you couldn't! A bi-directional line is where there is dual track (or more) and one or more lines is signalled for trains to run in either direction.

 

[Dr Hoo]

Sorry if this sounds a daft question.

Is it correct, that you can go either way on a single line. ?

Thanks

There have been unidirectional single chord lines. The Halton Jn (Runcorn) to Frodsham Jn line was one.
That line is now signalled for use in both directions.
The Merseyrail Wirral Line central loop is single and unidirectional.

So the answer to your question is “Not correct”.

 

[Ditop23]

There have been unidirectional single chord lines. The Halton Jn (Runcorn) to Frodsham Jn line was one.
That line is now signalled for use in both directions.
The Merseyrail Wirral Line central loop is single and unidirectional.

So the answer to your question is “Not correct”.

Thanks. I'm confused because in the rule book when talking about TSR'S and ESR's, it refers to single lines as going in both directions.

I think the other person said a single line is all by itself. But a bidirectional line will be next to another line, which may be bidirectional or one way.

 

[Gloster]

I would say that on the rare occasions that a single line is used in only one direction there would be specific indications that this was the case. If, in the rules and elsewhere, a line is just described as a single line then it is to be understood that it can be, i.e. is signalled or authorised, to be used in both directions.

A bi-directional line is one of a number of adjacent lines between A and B, but it is signalled or otherwise authorised so that it can be used in both directions, while the the other lines are just set up to be used in one.

Note: I am very much ‘old railway’.

 

[Annetts key]

The vast majority of single lines or lines classed as single lines even though they run parallel with other line(s) are bi-directional, that is, travel is permitted in either direction as part of normal operation. Hence the Rule Book treats them by default as bi-directional.

In practice, there are not many single lines that are unidirectional. The sectional appendix and the relevant signalling diagrams should show the permitted directions for normal operations for any running line.

Traditionally, if there are two running lines, they were by default, unidirectional, because that was the safest method of operation with no signalling, limited manual signalling or with mechanical signalling.

Now with more complex signalling, any line, whether single or one of a group can be signalled to be bi-directional.

Where a line (or part of) is under a T3 engineering occupation, all lines no matter what signalling is provided are treated as bi-directional.

 

[Supercoss]

Single Line = one line available for movements in both directions
-
Bi Directional Line = A line which the signalling allows trains run in both directions

source RSSB Glossary of Railway Terminology issue 6

 

[Dr Hoo]

Single Line = one line available for movements in both directions
-
Bi Directional Line = A line which the signalling allows trains run in both directions

source RSSB Glossary of Railway Terminology issue 6

That seems a very poor ‘definition’ if it’s unqualified. What sort of line is the Hitchin Flyover for example?

 

[Gloster]

That seems a very poor ‘definition’ if it’s unqualified. What sort of line is the Hitchin Flyover for example?

Agreed. By that definition a siding could be described as a single line. It wouldn’t surprise me if this is another example of people, probably non-experts/professionals, being so concerned to keep it simple that they lose precision and clarity.

Like the the misuse of Occam’s Razor: ‘the simplest answer is the best‘ sounds fine, but you must not forget the other half ‘…that fits all the facts’.

 

[Haywain]

What sort of line is the Hitchin Flyover for example?

It's part of a flying junction, so perhaps not a single line (I'm speculating).

 

[The Planner]

It's part of a flying junction, so perhaps not a single line (I'm speculating).

How its named in the sectional appendix would point towards how its seen to be.

 

[Supercoss]

Quite a few locations that have single lines with Bi directional signalling over it……..

 

[Haywain]

How its named in the sectional appendix would point towards how its seen to be.

It's in there as the 'Down Royston Flyover' and indicates that it is only available in the down direction. Quail (possibly an older edition) calls it the 'Down Cambridge Flyover'.

 

[MarkyT]

Single Line = one line available for movements in both directions
-
Bi Directional Line = A line which the signalling allows trains run in both directions

A typical single line, if allowing signalled movements in both directions, is also a bidirectional line, but it's not usually specifically named or referred to as such because it is the only track along the particular corridor and has signals for going both directions so it's obvious. In multitrack layouts, sometimes a line with this functionality may include 'birectional' or 'reversible' in its name to make its purpose clearer. From an interlocking perspective, whether a single line or part of a multitrack corridor, all bidirectional lines are treated in exactly the same way.

 

[norbitonflyer]

The word "line" is used in slightly different contexts in the two phrases. A "railway line" may mean a route between two points, having one, two or many individual tracks (eg the "East Coast Main Line") , or it may mean an individual track, as in the "Up Slow Line" .

A "single line", is an example of the former usage - a "bidirectional line" of the latter. Most single line railways are of necessity bidirectional (oddities like the Liverpool Loop excepted), so the term "bidirectional" is usually only used in a multitrack layout to describe a track which can be used in either direction - so approaching Peterborough from the north, the "up slow" is signalled for bidirectional use as far as Wennington Junction to allow trains from Spalding (which usually arrive into Platform 1) to return whence they came without having to cross the fast lines.

 

[RailwayRookie]

Somewhat of a huge oversimplification. But a single line would often be named in the sectional appendix as the 'Up & Down XXXX' where bi-di lines be more along the lines of 'Up XXXX' and 'Down XXXX' running as a pair, but signalled for movements in both directions.