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A guide to ACI (Automatic Car Identification)/Kar Trak labels

The ACI system consists of a series of 13 colour labels applied to the car side, drawn from the 13 labels below. Each is comprised of zones of four basic colour zones (red, blue, black, and the white checkerboard pattern), placed upon an all-black background. Line-side scanners could read the car's reporting mark and car number from these labels. In use from roughly 1968 to 1978, the system was discontinued due to reliability problems caused by missing, damaged or dirty labels.

Many ACI labels can still be found roaming the rails today. From the freight car enthusiast's viewpoint, these are very helpful as they show the reporting marks and car number as of the discontinuation of the system in 1978, although they are now getting rarer and harder to read. They can also provide car numbers on photos of sufficient resolution to read the label.

ACI Start


ACI Stop



0 (checker/blue)


5 (black/blue)


1 (checker)


6 (blue/checker)


2 (red/checker)


7 (checker/red)


3 (black/red)


8 (black/checker)


4 (red)


9 (blue)

ACI 10

10 (red/blue) — validity digit only

Each ACI label is 5-3/4" wide by 1" deep and is applied using a 3/8" gap between each individual digit. Sometimes the labels are applied directly to the car side, but more often applied to a black steel plate which was then riveted to the car side. I have an example of such a plate, which is 10-1/2" wide by 22" deep

Format of an ACI label

ACI labels are read beginning from the bottom, and is divided into the following six parts:

1. The first (or bottom) label in any tag is the start label.

2. The second label is the equipment code number. "0" is used for railroad-owned equipment, "1" for privately-owned equipment (reporting marks ending in "X", and "6" is used for non-revenue (or non-interchange) equipment (on CN at least). Other digits were reserved for diesels and piggyback trailers (I believe "2" was in use for piggyback trailers, and on Canadian National at least the digit "6" was used for online captive equipment such as OCS cars).

3. The next three digits are a number indicating the equipment owner, with each reporting mark given a separate number.

4. The next six digits are the car number, padded with leading "0" labels as necessary (i.e. a car numbered 432 would be labelled as "000432". Diesel labels replace the first two digits with the type of unit and suffix number.

5. The stop label will follow the car number.

6. The last (top) label is used for the validity digit. This validity digit is calculated according the following formula: multiply the first digit by 1, the second by 2, the third by 4, the fourth by 8, the fifth by 16, the sixth by 32, the seventh by 64, the eighth by 128, the ninth by 256, the tenth by 512. Add the results together and divide by 11. The remainder after the last full division by 11 (0 to 10) is the validity digit.

Eric Neubauer has compiled a list of the four-digit owner codes, which can be found at: www.enter.net/~eaneubauer/aci.pdf

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This compilation © 2011 by Ian Cranstone