Selective Compression

[steinjr]

we should be able to devise a rough rule of thumb to help us with this vexing question.

Byron Henderson has posted quite a few well articulated thoughts on compression in various forms on his blog:

"Selective compression" vs "compressive selection" - http://mrsvc.blogspot.com/2009/04/select...ssion.html
"Caricature, copy or close enough": http://mrsvc.blogspot.com/2009/06/carica...nough.html
"Perils of the prototype" (as part of the tricky traps of design series): http://mrsvc.blogspot.com/2006/11/tricky-traps-5-8.html
"Track plan analysis" - part 2 about train capacity, flow and balance: http://mrsvc.blogspot.com/2008/02/track-...dexed.html

As for rules of the thumb - it depends on what you are modeling and what scale you are in. Compression rules of the thumb are very likely different for a display layout vs a dispatching layout vs a switching layout (to use three rough descriptive terms), or for an N scale layout vs an H0 scale layout.

For a H0 scale switching layout in a bedroom sized layout, a train length of 7-8 cars often work well - and could be said to represent maybe a 30-40 train (which rhymes with the 25% figure posted above). It gives a train that is about half a wall length long, which gives you room to have a couple of train lengths between sidings.

But for an N scale passenger train rolling through the landscape, it is not a given that 4 passenger cars will give you same feel as a 16 passenger car real train. There I would guess that you would need to go to e.g. an 8 or 10 car passenger train.

For a H0 scale switching layout, handling cuts of 3 or more cars is often sufficient to give the impression of the train handling cuts of cars - as opposed to handling one or two cars. For a H0 scale switching layout, an industry often has a respectable size if it has 3 or more car spots.

What it comes down to in the end is to maintain flow and balance. Not putting together trains that will stretch through several scenes at the same time, not make trains so long that they cannot fit into sidings etc.

Another approach - more suitable for a dispatching style layout - where traffic flow is important - was taken by Roy Dorn, who formulated a set of formulas to calculate how many and how long trains a given track plan could afford (at the most). Joe Fugate has the formulas on his web page - here: http://siskiyou-railfan.net/e107_plugins...content.32

I once ran the calculations on a track plan just to see what the calculations said - they sorta made sense in that context:


Room area : 6.5 x 11.5 feet = 74 square feet
Layout area : 44 square feet (59% of room area)
Number turnouts : 30


Mainline track: 48 feet (96 cars)
Passing tracks: 11.3 feet (22 cars)
Roseville siding : 6 feet (12 cars)
Yard track 1(A/D): 5.3 feet (10 cars)
Staging tracks: 12.6 feet (25 cars)
Service tracks: 0
Storage tracks: 33.9 feet (67 cars)
Yard tracks 2-6: 18.1 feet (36 cars)
Industry sidings: 15.8 feet (31 cars)
Connecting tracks: 24' (48 cars)
Switches: 264cm (12 switches not already counted as part of main line x22cm)
Yard lead: 118 cm
Flour mill runaround: 2 feet
Other connecting track: 294 cm


Passing sidings: 2
Passing train length: 12 (max)/11 (avg)/10 (min) cars
Staging tracks: 2
Staging train length: 13 (max)/12 (avg)/ 11 (min) cars

Maximum number of cars: 105*0.8 = 82 cars
storage: 67
staging: 25
passing/2: 11
Number of cars moved: 124 * 0.4 = 50 cars
staging: 25*2 = 50
passing: 26
connecting: 48
Average train length: 11 cars (avg passing)
Trains: #cars moved (50) / avg train length (11) = 5 trains (really just under 5)
Dispatching threshold: (3x10 +2x11 +12)/6 = 10 car trains

Nuff random thoughts on the subject for the evening?

Grin,
Stein