Automatic equipment identification (AEI) is an electronic recognition system in use with the North American railroad industry. Consisting of passive tags mounted on each side of rolling stock and active trackside readers, AEI uses RF technology to identify railroad equipment while en route. History Predecessor systems In the late 1960s, railroads in North America began searching for a system that would allow them to automatically identify rail cars and other rolling stock. Through the efforts of the Association of American Railroads (AAR), a number of companies developed automatic car identification (ACI) systems. The AAR selected four systems for extensive field tests. General Electric developed an RFID system, ABEX a microwave system, Wabco a black and white barcode system, and General Telephone and Electronics (GTE) a color barcode system called KarTrak. The RFID system used a tag mounted under the rail car and an interrogator installed between the rails. The other three systems had labels that were mounted on each side of the rail car and a trackside scanner. After the initial field tests, the ABEX, Wabco, and the GTE KarTrak ACI systems were selected for a head-to-head accuracy test on the Pennsylvania Railroad, at Spruce Creek PA. The KarTrak system was declared the winner and selected by the AAR as the standard. The KarTrak system was abandoned by the late 1970s. Because of this failure, the railroad industry did not seriously search for another system to identify rail cars until the mid-1980s. Development Burlington Northern was the first railroad in North America to renew the search for an effective identification system. BN had been closely following the efforts of various maritime shipping companies, such as American President Lines, in their efforts to find a system to automatically identify containers. Based on the maritime companies' success with RF-based identification systems, Burlington Northern began a testing program in 1986. Burlington Northern initially asked nine vendors to present their identification systems. From this group of nine, Burlington Northern selected two systems for full-scale testing. The two vendors selected were General Railway Signal (GRS) and Union Switch & Signal (US&S). The US&S system is manufactured by Amtech Corporation of Dallas, Texas. In January, 1988, Burlington Northern equipped 1,500 taconite (iron ore pellets) rail cars in northern Minnesota each with a GRS and an Amtech transponder. Each vendor also installed three wayside reader sites. All tags were mounted on the sides of the rail cars.