Track crosssings

[ajaarm]

Some months earlier an article(perhaps Ask Trains)appeared,which explained the means used to determine what train would have right of way when tracks crossed one another.In some cases it would be a different railroad.If you recall what issue this was in please let me know;Thank you Jim W.

[Railway Man]

ajaarm

Some months earlier an article(perhaps Ask Trains)appeared,which explained the means used to determine what train would have right of way when tracks crossed one another.In some cases it would be a different railroad.If you recall what issue this was in please let me know;Thank you Jim W.

 

There is no general rule for crossings of two or more railways.  There is a specific rule for every at-grade crossing.  Priority for use of the crossing depends 100% on the agreement for that specific crossing between the two railways, which they negotiate however they wish.  The rule will usually be posted in the employee timetables or special timetable instructions for both railways, sometimes in the General Orders, and sometimes only in track bulletins. Some common forms of these agreements are:

1. First-come, first-serve.  The automatic interlocking and the "stop sign" crossing is the most common form of this.  An automatic interlocking has approach circuits on all four tracks.  Whichever approach circuit is first occupied gets the interlocking, and owns the interlocking until it releases it by exiting the interlocking.  If another approach has been detected in the meantime, it gets it next.  The stop sign interlocking requires any approaching train to stop short of the crosssing, verify there is no conflicting movement, then proceed.
2. Manual interlocking.  This is under the control of one of the railways.  Most manual interlockings today are remotely operated by a train dispatcher from a dispatching office, and for most practical purposes are identical to Centralized Traffic Control. The dispatcher determines which route gets priority, as he sees fit for the efficient movement of traffic, unless governed by superseding rules that say which railway gets priority.
3. Stop sign one route only.  The other route has right-of-way.  The stop-signed route must stop and can only proceed if it sees no conflicting or approaching movements on the priority route.
   
4. Most manual interlockings have agreements that specify train handling committments by the railway that operates it.  This is a frequent source of argument.

Crossings that are "same railway" can be stop-sign both routes, stop-sign one route, automatic interlockings, or manual interlockings.  The priority is as set out in the employee timetable.  Generally, crossings that are stop sign both routes or automatic interlocking are first come, first serve.  Crossings that are manual interlockings are per dispatcher discretion.  Crossings that are stop sign one route have fixed priority.

Often the special instructions will require the inferior route at a stop-sign one route only, or both routes at a stop sign both routes, to not occupy the crossing unless the train movement can be made in one continuous motion, or near-continuous, without occupying the crossing while switching.  Crossings that are signalized (automatic block, manual block) fall under block system rules that govern continuous motion and reverse moves.

RWM

[tree68]

I recall reading somewhere about a situation at an automatic interlocking where two trains hit the circuit at exactly the same time.  They both got red signals.  Who got to go first was decided by a flip of a coin.

[Railway Man]

tree68

I recall reading somewhere about a situation at an automatic interlocking where two trains hit the circuit at exactly the same time.  They both got red signals.  Who got to go first was decided by a flip of a coin.

 

Circuit designs for many years (since the 1930s at least) are designed to prevent that from occurring.  There are probably some old, very cheap circuits still in service that are not so equipped.  A couple of days someone was telling me they went into a B Case in Chicago a week ago to survey it for a PTC interface and the equipment inside dated to 1912. 

What often happens is the interlocking isn't working at all due to shunted track -- and had there been only one train, it also would have got a red signal.

RWM

[tree68]

The account was from the days of steam, so it probably went back that far.  The crews walked to the diamond to sort things out.