202410 – Burns – Designing the Layout

Railways exist to meet operational needs.

The classic Signal Education starts with determining how to position some signals on a layout. The laying out of the signals determines the capacity, we are told. But there are quite a few process steps and quite a bit of design which must occur before there are signals to lay out.

The Signal Engineer cannot create a facility that the layout does not support.

Operational requirements start with what the passengers need in order for them to decide to travel on the railway.

Important to passengers will be (a) how many passengers can my layout transport per period of time (capacity), (b) what end-to-end travel times (looked at from the point of view of the passenger, not the train) are offered, and (c) what interchange facility is provided at start, midway (where needed), and at the end of the rail portion of the journey.

“Build a Metro” provides one route to answer such requirements, but there are many other more appropriate types of railways which can meet customer needs better than metros in particular situations.

Which situations?

A Metro is an example of a railway whose strategy is “saturating the roads”. But there is another strategy available called “saturating the nodes”. Anyone who has travelled by rail in Switzerland will have seen this strategy in action. It is also possible to adopt a strategy which is a hybrid of these two approaches.

A practical case example will be provided of what a “saturating nodes” solution would look like for one Australian Capital city.

Returning to the “Metro” concept, the first necessary step beyond the classic configuration is to support a junction. The headway aspects of junctions and the timetable constraints they impose are key to ensuring a metro (one with roads which are actually saturated) can provide its required capacity.

Two simplified illustrative examples will be considered.

The first will be the loop with diamond junction of the type originally present for the Clifton Hill Loop in Melbourne. Headway requirements for the diamond junction will be looked at together with the timetable transit time constraints imposed.

The second example will be the “split centre loop” type of the sort found on the Northern Line in London. Transit time constraints for the centre section will be the main focus here.

These two examples introduce the concept of “resonance” as a required component in timetable planning if capacity is to be achieved without needing to endlessly build new parallel tracks. The question as to why getting the trains to run on time is key to achieving capacity will be answered along the way.