Is there an order to freight cars other than when they will be dropped off?

Good question for discussion. I'm sure you will receive quite a few responses.  The era that you are modeling has a lot to do with it. There are safety issues, especially in the current era. There are also "blocking" and lighter and heavier car concerns .  A local crew will order their train to minimize switching on their job for the day.  This thread should be very informative.    I'll let some of our professional members tell you what they know from experience.  I do know that "back in the day" the most important rule was DO NOT PUT THE LIVESTOCK CARS RIGHT IN FRONT OF THE CABOOSE/CABIN CAR !  :-p         

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Asked and answered:

How do RR's choose the order of freight cars? | O Gauge Railroading On Line Forum (ogaugerr.com)

Arthur, thanks for the link, but in six years since the last post in the other thread, there could be some new information worthy discussion, especially with the new fangled mega trains.

Railroads do have blocking protocols. Hazmat products in particular must be blocked according to protocol so that cars containing certain hazmat classes aren’t placed in a train adjacent to cars containing other hazmat classes with which they may adversely interact in the event of a derailment.

For example, my former employer manufactured sodium chlorate, an oxidizer used in the bleaching of wood pulp. Cars containing sodium chlorate could not be placed in a train adjacent to cars containing acid as commingling the two would cause an explosion.

Curt

Our trains often carried loads labelled “explosives A” and had be precisely in the middle of the wheel report.  There would be a separate train order in our clearances indicating we had an explosive load. Our “dangerous cars” had to have five other (non-dangerous) cars between them and the waycar or locomotives.  Just a few of many examples…

@Rob Leese posted:

Our trains often carried loads labelled “explosives A” and had be precisely in the middle of the wheel report.  There would be a separate train order in our clearances indicating we had an explosive load. Our “dangerous cars” had to have five other (non-dangerous) cars between them and the waycar or locomotives.  Just a few of many examples…

Yes, we used to have a red card attached to the waybill of such cars. We called them "Blow Up" cards!

Freight trains are also made up to avoid excessive in-train forces.  Each railroad has its own blocking rules on this, but the main focus is to avoid having a heavy block of cars behind a series of light cars, so that the tonnage on the rear could not pop a light car off of the rails if there were a run-in of slack, or break a coupler if there were a run-out of slack.

Think of it as 20 cars of bowling balls at the rear of the train,  behind 20 cars of straw hats, and all cars are equipped with sliding drawbars (end cushioning).  You want to avoid that.  It's more important than having every car in station order, even if it means making a pickup or a  setout behind other cars.

Tom raises an interesting point regarding “buff and draft” and empty cars.

In a similar vein, the aluminum sparger covered hoppers we used to transport sodium chlorate were very light compared to a comparably sized steel covered hopper. Our aluminum cars were equipped with devices to govern the brakes on the cars when they were empty. The idea was to prevent the wheels on an empty car from “locking” and sliding on the rail during brake applications.

Curt