Railroad Museum of Virginia

nw-mailing-list at nwhs.org nw-mailing-list at nwhs.org
Wed Nov 1 23:07:23 EST 2006

Viewing this caboose brought back memories to me. If one looks closely to
the right of the "NW" one can see a painted-over ACI (Automatic Car
Identification) label. Many of you can remember seeing these colored labels
on both sides of equipment in years gone by, or in old photos from that era.
In this Sylvania developed system, each stripe was coded in red, blue and/or

Reading up from the bottom, the first stripe was a "start" stripe, and the
next four stripes represented the reporting marks (0550 as assigned by the
AAR for the N & W as best I remember), the next six stripes represented the
equipment number (518666 in this case) and the penultimate stripe was a
check digit that was a mathematical derivation of all of the other numbers.
The last stripe at the top was a "stop" stripe.

The stripes were retroreflective, meaning that they reflected a light from a
scanner straight back into the scanner. Each wayside scanner used a fast
vertically rotating (1750 rpm as best I remember) wheel with multi-faceted
mirrors on its periphery that reflected a internally generated beam of light
to scan the label from bottom to top several times even at high train speeds
past the scanner. The light was reflected back into the scanner where
sensors detected the red, blue or white codes and converted these into the
reporting marks and equipment number. This information could be used by a
railroad to determine the identification of each piece of equipment in a

Although initial tests verified the technical proficiency of the system
before it was mandated by the AAR, after about 1-1/4 million cars had been
equipped, experience revealed that the read rate in service was less than
expected because of dirt buildup on the labels as well as occasional label

I served on an AAR Technical Task Force to see what could be done to improve
this optical system. We considered several possible solutions without
sufficient success.

The AAR then formed a Task Force for New Concepts in ACI. I served on this
committee also, and we considered all known systems for equipment
identification, finally narrowing the search to a system using microwave
scanners to interrogate passive responders on the equipment. This is the
system that was subsequently adopted by the AAR, and is currently in use,
having replaced the optical system after tens of millions of dollars had
been spent on the latter.

A little bit of history for those who have wondered about these colorful

Gordon Hamilton

----- Original Message -----
From: <nw-mailing-list at nwhs.org>
To: <nw-mailing-list at nwhs.org>
Sent: Wednesday, November 01, 2006 9:48 PM
Subject: Re: Railroad Museum of Virginia

> Picture attached: Norfolk & Western C31P caboose 518666 in

> downtown Portsmouth, VA.


> Jerry Kay, Portsmouth




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