Operations SIG Operations PRIMER (FAQ)
Freight Car Fleet
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1. How does one determine the number of cars needed to
adequately operate [fill] a layout?
Question 1: I'm unsure how one determines
the number of cars needed to adequately operate [fill] a layout. Is there
some formula to determine car quantity based on sidings, staging, main line
footage, yard tracks, etc.?
Answer 1: I don't know of a 'formula' for estimating car
requirements. I think most people keep buying and building cars and putting
them on the layout until they realize they are approaching gridlock, then
they start winnowing out the weak sisters. But to quantify it logically,
one would take a mental snapshot of the layout at a given moment, for example,
as of the end of an operating session. There will be x many staging tracks
holding x many cars; the online industries will have a car-spot capacity
of x, perhaps on average 50% occupied; and there may be interchange tracks
holding x many cars. In addition to these 'stationary' cars there could be
some cars left over still en route, either in yards, 'off spot' in towns,
or even in trains stopped along the mainline. These could be counted by
thinking through the events under way or not yet complete at that moment.
For example, there could well be cars that came into the yard during the
'day' that won't go out until 'tomorrow's' local is made up.
Another dimension of this would be, what types of cars are needed?
Part of the answer comes from what kinds of online industries will be
using them (or, what kinds of industries shall we build to utilize our
cars)? If your railroad has significant 'overhead' traffic (from offline,
to offline) it can be made up of more varied car types, within reason.
There are statistics on the types making up the national car fleet, not
to mention the fleets of each individual railroad, but that has only
limited relevance to your layout's particular traffic flows.
Just to complete the picture, the ownerships represented could also
bear some thought. This could be one of those subjects about which one
might not wish to know too much, but it is true that while freightcars
could go anywhere in the country, in fact they tended to stay more or
less close to 'home,' more so for hoppers and gondolas, less so for boxcars
or reefers. While perhaps subtle, the ownerships of the cars appearing on
a given layout should tend to reinforce the impression that this is New
England, say, not southern California. It has been suggested as a rule of
thumb that around 50% of cars on line should be 'home' ownership, but this
can vary substantially depending upon the type of operation, ie. branchline
(more), overhead traffic (less), etc.
Finally, the issue of 'era' bears mention. The appearance of a yard
full of freightcars changed gradually over the years so that there are
significant differences between the 1940s, say, and the 1980s. Again this
is something that may not bother one until he/she becomes aware of it.
Not only were 36 and 40-foot cars replaced by 50 and 60-footers, and roof
walks largely outlawed after about 1970, but even the road names changed
as the merger movement took effect. Cars can be approximately 'dated' by
reading the small print indicating built or repainted dates. Again, there
is a fair amount of flexibility here, but more extreme anachronisms should
Page updated: 2006 January 21