In its earliest form, these trains were a collection of 89ft piggyback flats moving from a terminal with too many to another terminal in need. This is usually caused by an imbalance of trailers and/or containers moving into one area and moving out by another means. For example, Oakland loads more containers for export than come into the port as imports. Many steam ship lines have the schedule set for the ships (vessel string) to unload first in Los Angeles or Long Beach then move to Oakland for final loaded before heading back to Asian ports. As a result, Oakland accumulates a lot of empty well cars. About every other day or so, BNSF will run a whole train of these empty wells to the San Pedro harbor terminals where they can be put to use.
Another example is the single stacking of westbound marine stack trains loaded with grain and soybeans for Asia. This moves more wells to the West Coast than containers. To move the remaining containers, the railroad will run a collection of empty wells (bare table train) from the LA area to Kansas City (LPK) or Chicago (LPC).
This also occurs with trailers and containers moving into certain markets. Denver and Phoenix are two prime examples. Both are consumming cities meaning that more products are shipped in than are shipped out. About once a week the railroad will load an entire train with empty trailers and containers and move them back to the LA area for loading. These trains may at first look like a regular Q or Z train. The clue is that the trains generally only have two units for a mile long train. Most Q and Z trains have 3 to 5 units for the same length train. The other clue is the way the train is loaded. For example, on most Q and Z trains the containers from the three primary trucking companies JB Hunt, Schneider, and Swift are mixed together as this was how they entered the terminal in a fairly random order. But when loading empty containers, they are usually loaded in groups by trucking comany. This makes it easier loading and unloading. So on baretable trains with containers or trailers, you will see a group from one trucking company, then another group from a different company. Here are four examples of bare table trains that repostition truck trailers and containers.
BABQLAC4 from Albuquerque usually has 2 units with around 15 wells of UPS boxes. It is mostly spine cars with UPS vans, UPS boxes, a few other vans like Xtra, McKinney, Premier, some plain white vans, and may have a few JB Hunt boxes. It runs maybe once a week and has been spotted on either Monday or Tuesday.
BCHILAC4 from Chicago runs occasionally and the one time I saw it was on a Thursday morning. It had 2 units with 111 wells of mostly JB Hunt, 8 Swift, 28 CH Robinson, 2 UPS and 20 plain grey containers.
BDENLAC4 runs about once a week. It usually has 2 units and 75 to 95 wells of mostly JB Hunt boxes. Trains may include some (maybe up to 18) Swift, and occasionally Schneider boxes. The train may run either on Sunday in the evening or Thursday in the morning. It may have empty wells at the rear.
BPHXLAC4 runs about once a week. Here is what I saw on one Sunday evening from the Hesperia cam. Three units, 16 UPS vans on spine cars, 8 wells 16 JB Hunt, 7 wells 14 FedEx, 3 wells 4 Matson, 2 white boxes, 18 wells 36 Schneider, 9 wells 18 JB Hunt, 5 wells 2 FedEx, 1 Swift, 7 white boxes, 12 wells 1 CH Robinson, 23 UPS, 3 wells 5 Swift, 1 UPS, 13 wells 26 Schneider.
I think these trains setout part of the train at San Bernardino and the rest are for Hobart Yard in Los Angeles. So you will often see two groups for each truck line on each train. Notice in the train above that there were two big groups of JB Hunt and Schneider containers. San Bernardino is more of a FedEx hub and LA is more of a UPS hub.
Intermodal terminals that send or receive baretable trains are:
LAC Hobart Yard in Los Angeles
LPC Logistics Park in Joliet (southwest of Chicago) mostly 40ft wells for marine containers
LPK Logistics Park in Gardener, KS (southwest of Kansas City)
NSI Norfolk Southern Interchange in Chicago
OIG Oakland International Gateway in CA mostly 40ft wells for marine containers
SBD San Bernardino, CA
STO Stockton, CA
A typical symbol might be the BLPCLAC5 with 40ft wells for marine containers. If the section number is 7 then the cars are 53ft wells for domestic containers, 1 is used for spine cars, and 4 for empty truck company containers and trailers.