Now there are some interesting numbers. Your line basically has 1 locomotive per 6 freight cars. One could make 108 six car trains. That is not terrible. I've always wondered if there are ANY model railroads out there what have a balanced fleet. My ratio of locomotive to freight cars is way out of proportion. And my ratio of passenger cars to freight is also out of whack. At one time I am guessing my loco to freight car was down to 1 to 1.108 diesels (94 are union pacific engines)
613 freight cars
The Union Pacific, a railroad known for having too many locos, has 8,000, and 64,191 freight cars, or 1 to 8. BNSF has similar 8000 locos but almost 90,000 cars, or 1 to 11.
BUT these locos do not just move railroad owned cars. I am guessing that fewer that half the cars on the system at any given time are their own. Think of all the other railroad cars in interchange. Seven class ones interchanging equally would yield some challenging calculations. Then all the private companies out there (chemical companies UTLX, general transportation ABOX, all the power companies APOX, grain companies CGCX, etc. ). Simple on-line searches have not been helpful. I am guessing the ratio is at least to 1 to 20. Someone should do some research and write a scholarly work to submit to the model railroad related rags.
And then of course there is length of rail to loco ratios to talk about/consider. For me with zero rails the ratio doesn't even work since division by zero is undefined.