What does the x mean in locomotive road numbers, eg X3985? Does it have to do with it being "retired?"

Question

What does the x mean in locomotive road numbers, eg X3985? Does it have to do with it being "retired?"

Answer 1

I see your example number is that of the restored UP "Challenger" class of locomotive, an articulated steam engine with a 4-6-6-4 wheel arrangement.

In this instance, the "X" before an engine's road number designated it as an "Extra" train.  

Trains that used to be identified as a "Regular" train, which is one that received its track authority and ran under a timetable schedule, carried the number of the train on its number boards, such as 102, and not the engine number.  The engine number would have appeared on the train orders.  It would have been instructed to display "No Signals" on its clearance.  The signals referred to being the illumination of class lights, and where there was more than one section running on the same timetable authority, all would be instructed to display "green" signals indicating that there were following sections.  In this instance, the number boards would indicate I-102, 2-102, etc.  The last of these would display no signals.  Only then had the train, with all of its sections, passed.  This was done regularly as ridership was high and regular trains often needed to be ran as two sections to accomodate overflow passenger traffic, or a special running on a regular train's schedule.

Any train not authorized by timetable was an extra train, receiving its authority by "Train Order," and would display white signals with the class lights.  Its number board would have read, X3985.  It is a safe bet that in this instance the Challenger, having been restored, is carrying the number board X3985 merely for historical accuracy, as there are no longer any trains designated as an "extra" or "work extra."

A "Work Extra,"  still displayed white signals, but its train order authority was slightly different than for an extra train, giving it authority to operate in two directions, such as out to one point and back to the starting point.  Extras were authorized to operate in one direction only.

Answer 2

If it's permanently painted on the unit, that might mean retired.  If it's changeable number boards, it almost certainly designates an "Extra" train, as Hoghead describes.  

Scheduled trains have permanent numbers in the timetable - Amtrak 6, the California Zephyr.  When a train isn't scheduled, it's called "Extra" and the number is that of the engine pulling it.

If I recall, 3985 is the number of a famous, restored steam engine used for excursions around the country.  Such excursions are not scheduled, they run as "Extras".  

3985 does, in fact, have changeable number boards intended to label the train it's pulling.  (for instance, if 3985 was pulling Amtrak's California Zephyr, those numbers would be changed to "____6".  Since excursions aren't scheduled, 3985's train is usually labeled "Extra 3985", thus, X3985.

Answer 3

Absolutely.  Many times, the number series a locomotive, or several locomotives, occupied during their active service, is currently used by newer locomotives.

Rather than put new reporting marks on them, the railroad will just put an 'X' in front of the number.  The restored engine gets to keep it's original number, and the active fleet doesn't require any number shuffling.