Daria,
What are you really trying to get at?
Prior to the modern merger movement, say before 1968, routing was a big deal and could be very obtuse, or could invlove several carriers working together as a single route in terms of tafffic solicitation and operation.
Today the shippers still have the "right of routing", but the carriers have the right to not offer "turkey trail" routes that contributed to the complexity of former times. The practical effect of mergers and route closures has been to concentrate transcontinental interchange at Chicago, St. Louis, Memphis, and New Orleans.
In most cases the shipper is located on one of the Class 1 (big) carriers. If distination is on same carrier, the traffic is said to be local and how the traffic moves is up to that carrier. In general it will move by the lowest cost route, which is often the most direct.
If interchange is involved, it is either with a short line or another class 1. The shortline interchange is unusally at one specific location, so logically is not much different than the local case. If interchange is with another Class 1 at a trans mississippi point, the possibility of alternate routes arises.
I worked for a shortline in northwestern Oregon for a while. We were in former SP territory and interchanged with SP at Eugene and Albina (Portland). We had instructions from the UP to route cars to northern states east of its own system via Albina, and to southern states east of its own system via Eugene. I would be willing to bet that our cars to Albina went to North Platte where they were sorted for interchange at Chicago. The others went via the Sunset Route for interchange at New Orleans or Memphis.
One thing to note here, before the UP takeover of the SP, ALL of this traffic would have moved to Eugene, then to Roseville. At Roseville some would have gone east over Donner Pass to the UP at Ogden, and some would have stayed on the Sunset Route to New Orleans or Sunset Route to Texarkana then SSW (Cotton Belt) to Memphis and St. Louis. The route from Oregon to Memphis and St. Louis was not the shortest route, but since SP owned about 99% of the stock of SSW it was the SP system long haul, which the ICC allowed the origin carrier to use as opposed to short hauling itself.
Back to modern practice, the class 1 carriers as a group will first protect their long haul, and then prefer the shortest available main line route.
There are three notable exceptions to the trans mississippi interchange point pattern. The NS owns a line extending west to Kansas City. The KCS, acting in concert with and partially funded by NS, operates a line from the Dallas TX area to Meridian MS. On the map this is a classis bridge line that neither originates nor terminates the overhead traffic. In marketing terms it is a NS incurstion into western territory. It works because it keeps traffic out of the more congested Memphis and New Orleans. The other incursion is BNSF to Birmingham Alabama.
One final complication is reciprocal switching. Within defined limits railroad A will switch cars to its customers for railroad B, or C, etc. To the extent this allows the customer access to a line haul carrier that goes where his traffic needs to go when the serving carrier does not serve the destination, it is a mutually beneficial arrangement. To the extent it lets the customer play off two or more carriers in terms of rates and service, the advantange is all to the customer. Due to the extra handling involved in the terminal, transit time via the non-serving line is almost always longer than via the serving line.
If you know origin and origin carrier and destination and destination carrier and which lines are main lines as opposed to branch lines, and a bit about each carrier's internal flows you can just about predict how the traffic will move anywhere in the US.
Mac
No.
OTOH, most freight haulers try to keep freight on their own road, so if CSX picks up a car in Chicago, bound for NYC, it'll stay on CSX rails. A car from Chicago to NYC on NS will take a different route, again staying on NS rails.
The through routes are fairly simple these days, as opposed to years ago, when such a routing might travel over several railroads.
A rail atlas such as SVP would probably suffice.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Is there a tool/app that can show the route that freight train would take to move freight from a given origin to given destination point? Something like Google Maps directions, but for railroads?
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