Freight Car Friday – Tracking Trains; Automatic Car Identification

13 12 2013

At any moment, there are tens of thousands of freight cars on the move across North America today, each with its own destination. A single freight train entering a yard may have cars for more than a dozen outbound trains. How do the railroads keep track of it all?

For a long time, it was all done by hand with paper forms physically handed from one yard operator to the next. The process to automatically track freight cars, and thereby their contents, began in the late 1960s. Today, the railroads have taken this process into the digital world. Shippers can find the location of their freight with the click of a mouse on a website. And while the role of conductors and office clerks remains, theirs is now a world of computer screens and servers, not row upon row of filing cabinets filled with carbon-copies.

ACI (Automatic Car Identification)

ACI tag

ACI tag

The first attempts at tracking cars were similar to the way a retail outlet tracks their inventory – a bar code. Unlike the black and white bars of varying thickness used on just about every product sold today, the ACI tags used a set of 13 bars in 12 combinations of 4 colors. There were color combinations for digits 0-9, a validation number and start and stop tags.

The tags were read from bottom to top. After the start code, there were four digits which corresponded to an assigned number for the railroad (or private owner) reporting marks. Then there were six places for the road number. Above that came a stop code and a validation number code.

The system was developed by KarTrak in the 1960s and in 1967 the Association of American Railroads mandated that the placards be applied to all equipment. This included freight cars, locomotives, maintenance of way, even piggyback trailers – anything that would pass the scanners and could be tracked. Tags were to be applied to everything by 1970.

covered hopper

This PTLX covered hopper, built in 1975 still has its ACI tag in 2011.

To implement this, the custom tags had to be fixed to everything in relatively short order. This is not as simple as it sounds when that equipment is scattered all across the continent. It was not uncommon for a general service freight car to stay away from home rails for more than a year at a time.

Once the cars arrived at a terminal with the tags, they had to be sent to the car shops for the application. Some tags were adhesive stickers which could be placed directly on the car. Most were applied to steel plates which were then riveted or welded on. This was especially true in colder months when the stickers apparently did not adhere well to the cold steel. Excessive dirt on the car also had to be cleaned for a good fit. And of course both sides of the car had to be tagged and at the proper height.


Zooming in on the PTLX car, the modern AEI tag can also be seen just below the side sill. Note the visor welded above the ACI tag to help shield it from the elements.

Once tagged, the cars could be read by trackside scanners. Scanners could read the tags at up to 80 mph and operators would have an accurate account of what was in each train and where any car in the system was located within minutes. Scanners were typically placed at the entrance to yards and junctions or interchanges where updates were most useful.

Unfortunately the system never reached its full potential for a variety of reasons. First, the tags were easily obscured by dirt (the railroads didn’t have the graffiti problem they face today fortunately.) They also frequently fell off from improper application or were burned off from hot loads (gondolas in hot steel service) or car heaters (hoppers.) And of course, despite the best efforts, there were many cars that never got their tags.


AEI tags can be a tool to uncover the original owner and number of older equipment.

By some estimates, the system only worked about 70% of the time at its peak. Railroads like the Union Pacific put car inspectors back at the entrance of yards to record the numbers of each car in passing trains as a backup to the system. The practice of adding and maintaining the tags was officially discontinued in 1978, although some railroads did continue to add tags to new cars and use the tracking equipment for a few more years for what it was worth.

While the tags weren’t maintained after 1978 (that is probably being generous!) they weren’t immediately removed either. Some can still be found on cars today, although the number of cars still in service from those years in shrinking rapidly. As cars changed owners the tags stayed the same. Even when repainting cars, the tags were often simply covered with the new paint – often only to have it peel off soon after. For the freight car historian, these can still be a great help to track a cars original owner and number.

AEI (Automatic Equipment Identification)

Same concept, different technology. Fast forward twenty years and railroads again turned to new solutions to help automate this immense challenge. Burlington Northern was the first to look at a new system in 1988. Theirs was based upon a similar concept already being tried by American President Lines for tracking containers.


The modern AEI tag is much more discreet but even more effective.

After several years of testing and committees by BN, other railroads and the AAR, standards were finally released in 1992. By the end of 1994, all of the rail equipment in North America was to be equipped.

AEI doesn’t use a visible bar code but rather an electronic reader. These are in some ways like the employee badges found in many places today which act as a key for coded electronic locks.

While they don’t need to open any doors, as the plastic tags pass the scanner, their identity is read and communicated to all parties. Like the ACI tags, these AEI trackers are to be applied to everything. They are much more discrete than the older version – just a small grey plastic module. They are usually placed near the frame or side-sill of the car.


An AEI scanner stands watch along Norfolk Southern’s mainline in Cleveland. The small white bars are the tag readers.

The new tags are not hampered by weather, dirt, graffiti or heat. Better still, they can be reprogrammed if the car changes numbers or owner. Today, if you look closely, you’ll find them attached to just about everything on the rails. Intermodal equipment is no longer covered under the plan. Railroads can however still identify the location of a trailer or container by locating the car upon which it’s loaded.

While these technologies are seldom noticed by the public – even the train-loving public – they have made a huge contribution to the success and efficiency of today’s railroads. Freight car technology is no longer simply a matter of types of steel or journal sizes. Railroads have learned to embrace all sorts of new technology to keep the trains rolling and the customers smiling.



One response

13 12 2013
Thomas Boden

It was an interesting article starting back in the 60’s with the ACI then to update to the AEI which very similar to what the military use on shipping container, vehicle’s, equipment.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: