What exactly is a Unit Train...?

Many people I know, who are model railroaders, say a unit train is a train consisting of a single type of car, tank cars, coal hoppers, grain hoppers, you get the idea. Although close, this isn't exactly true. One of the best explanations I've read is by a person named dehausman (sorry but that's all I have). It was presented on the Model Railroader Magazine forums in a discussion of mixed 50 and 70 ton hopper trains. He centers the explanation on coal hoppers but as you can guess it applies to all types of rolling stock.

By strictest definition then, what exactly is a Unit Train?

A unit train is a train billed on a multi-car waybill. It will have blocks of cars, typically 25-50-75-100-100+ cars all billed on a single waybill, which means all the cars on the waybill go from the same origin to the same destination. The multicar waybill did not become popular until the 1960's and 1970's.

Unit trains can have railroad owned cars or private cars. The cars can have a painted panel or not. There are standard steel hoppers, auto unloading hoppers, rotary gons, combination rotary and bottom dump hoppers. Standard hoppers can be bottom dumped or rotary dumped.

For a 1950's layout there would be coal trains, but not unit coal trains. There would be a 100 car coal train with 100 cars with 100 waybills, all of which could go to a different destination. On a unit train there would typically be 100 cars and one waybill.

The mix of cars depends on who the customers are for the coal. It was common for railroads to collect coal cars at a central yard and build solid coal trains to some destination where they would be switched and sent to the final destination. For example on the Erie it could be some major city. In the 1950s a city would use a lot of coal so the Erie might send 100 cars of coal to a city and the yard there would switch it up and put the coal cars on 10 different locals to be delivered to 40 different customers. Or the entire train could go to one customer such as a steel mill or a rail to water facility.

Seventy ton cars actually became popular in the 1920's. The PRR, B&O and NYC all had lots of 70 ton coal cars in the 20's and 30's (the PRR had more H21 hoppers than some other roads had cars of all types).

dehusman on MRR forums

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JMRI Error Codes - Causes and Possible Fixes (for the frustrated)

JMRI Error Codes - Causes and Possible Fixes (for the frustrated)

This was taken directly from the JMRI help documentation here. Thanks to all the great work the extensive number of developers and writers do on this indespensible product.

Anytime you have to contact the JMRI User Groupe please furnish all information at your disposal such as JMRI version, DCC system type, command station type and anything else you think is relevent.

301 - No locomotive detected

The command station has reported that it doesn't see a locomotive on the programming track.

This can happen if the locomotive isn't making good electrical contact or if there's a wiring fault in the locomotive. Or the decoder is having a problem.

302 - Programmer busy

The command station has reported that it's busy doing something else, and can't do any programming right now. This usually means that some other part of the DCC system is doing a programming operation, e.g. a hand-held throttle.

Some DCC systems can't do ops-mode programming (programming on the main) while also using the service mode programming track, in which case they'll return this error message.

303 - Requested not implemented in command station

This means that JMRI has requested the command station do something that it doesn't support.

This is not supposed to happen, as JMRI should disable programming modes that the command station can't provide. If you do see this message, please report the circumstances on the JMRI users Group.

304 - Aborted by user

The user has requested that the read or write operation stop early.

This is considered an error, because the program doesn't know whether the decoder actually saw the operation complete or not.

305 - Confirm failed

Some command stations allow you to "confirm" the content of a CV, rather than read the value from it. In general, this is faster than doing a complete read. If the value in the CV doesn't match the expected value, this message is issued. It's considered an error because if the values don't match, we know that we don't know the correct value for the CV contents

306 - Timeout talking to command station

The program did not hear back from the command station when it expected to.

This is by far the most common error message when people first start using JMRI. In that case, it usually means that the connection to the command station isn't correct. This could be a problem with the cable(s) making the connection, or a problem with how the preferences are set. Picking the wrong serial port is particularly common.

Once JMRI is working properly, this error may occasionally happen due to a transient error. DecoderPro generally will retry it successfully in that case.

307 - Unknown error

An error has happened, but JMRI doesn't know enough about it to be able to report more detail.

In general, JMRI is pretty good at deciphering what went wrong, and this message isn't very common. If you do see this message, please report the circumstances on the  JMRI users Group.

308 - No acknowledge from locomotive

At the end of a CV read or write operation, the locomotive replies ("acknowledges") to the command station using a pulse of current.

If that pulse isn't seen, some command stations provide this error message. It could be due to poor electrical connections to the programming track or within the locomotive. It could also be that the decoder doesn't support read back.

Some decoders, particularly certain sound decoders, draw so much current that the reply pulse isn't detected by the command station. In that case, one of the various "programming boosters" may solve the problem.

Author's Addition - Current Keepers/Keep Alives can also cause this error by preventing the return current pulse from being generated back to the command station.

For more information on programming decoders and how to work with Keep Alives and Current Keepers read this article.

309 - Short Circuit on Programming Track

The command station has reported seeing a short circuit on the programming track. That prevents programming operations.

Check the electrical connections to the programming track, and also within the locomotive.

310 - Sequence Error

For some reason, the programming operation ended early and the command station returned to normal mode (left service mode) before it should have.

This error can occur when some operations are performed in JMRI during programming. Turning track power on during a programming operation on an XpressNet is one example of how to create this error.

If you haven't performed any operations durring your programming sequence, this error, might indicate that you've selected the wrong command station type in the preferences. Check that. If that's correct and it's still happening, ask for help on the JMRI users list.

311 - Communication Error between PC and Command Station

The data between the PC and the Command Station was corrupted and the corruption was detected before the Command Station processed the request.

If this error occurs frequently, this error might indicate a problem with the connection between your computer and the command station or an issue with your system interface. Wireless connections are more prone to this issue than connections with physically connected cables.

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If you have an idea for a blog post here, let me know. If I can comment on it, I will or I'll see if someone else can and post it.