Several technologies made rapid advances during World War II and at the end of that conflict, considerable research continued into possible peace-time applications. Principal among these advancing technologies were aeronautics, computers, medical advancements, microwaves and nuclear energy. In the microwave field, the wartime application had shown that using microwaves could improve radar technology and provide increased accuracy over longer distances. In addition, radar miniaturization made it possible to install reliable radar equipment on moving vehicles, as well as to detect motion using radar.

Radio Corporation of America (RCA) was one of the firms that continued to conduct investigations into peace-time applications of wartime technology. RCA had a long history of strong commitment to research, having expanded its technical research division during the depths of the depression.

Interest in the development of jointless track circuit for signaling using radar technology caught the eyes of Chicago Rapid Transit Company (CRT) engineers immediately after the conflict ended. Dialogue with the industry on how this technology could be applied to the rapid transit continued for a few years, extending into the early days of the CTA.

The December 1948 edition of Transit News (an internal CTA magazine) carried a news item that noted that several months of study, research and preliminary experimentation by CRT/CTA personnel was to culminate in field testing of radar technology for rail signaling. A $35,000 contract with RCA and Television Associates was executed with testing of the technology to occur on a mile-long section of straight track. CTA noted that it hoped to provide maximum safety for operations, while at the same time obtaining greater flexibility in train movement. The news item concluded with the observation that a preliminary estimate for the radar-based signaling system was half that of conventional signaling.

Ben Feely provided the authors with a copy of the RCA report that indicated the first-phase testing of Electronic Range Indicating System (ERIS) was indeed radar-based. However, for radar to be accurate (maintain signal integrity), waveguides would have to be used in the tracks. These waveguides would direct the electro-magnetic waves through precision channels. This would have been difficult, if not impossible, to achieve through turnouts and crossings. Further, each train had to have a transmitter at the front connecting to the waveguide, and a terminator at the rear connecting to the waveguide.

The difficulties of applying this technology to a real-world rapid transit system resulted in the transition in the second phase of the study to a system that relied on pulsed transmissions (like those used in radar). Insulated joints still separated the wayside sections. In many ways, this second phase of the ERIS testing is the forerunner of what would happen 20 years later with cab signaling.

Field testing on ERIS began in November 1948 and continued throughout 1949. ERIS would transmit information on track occupancy ahead through the running rails, receiving this information from a series of wayside transmitters. Each wayside unit received the signal from the next one down the line. The transmitter would then amplify the signal and add to it as appropriate.

The signal information was transmitted as a series of pulses, with additional pulses added as required. Depending on the number of pulses received, equipment in the cab would then display a red, yellow or green indication. Unfortunately, no photos exist of the in-cab equipment.

CTA 4427 was photographed by Barney Stone near the end of track to the west of the Marengo-Lake station in Forest Park in late 1948. The shield covering the signal pick-up coil on the car is visible in this view -- it is the vertical piece hanging below the car on its right-front side. Multiple coils were originally proposed to be used.

Testing was not scheduled to occur on the Lake Street line, so perhaps this photo was taken immediately after the car had received the ERIS equipment, but before testing began. Only one car (the head car of the following train) required the test equipment to support field testing.

The final report for the ERIS tests noted that field testing began using the center track on the Jackson Park branch -- the east end of that track is shown in this view looking east into the Dorchester station during the testing.

After that, testing moved to the South Side Mainline middle track and then up to the area around Sedgwick on the Ravenswood.

A final report on the test program was issued with a December 1951 cover date. The report indicated the testing had been successful and that the program should advance into the next phase of testing. Despite this apparent positive outcome, there is no further evidence of continued testing on the CTA.

Barney's two photos of the equipped car and the testing on the Jackson Park had gone unremarked for 70+ years in the Krambles-Peterson Archive, except for George Krambles's notation on the back referring to the "radar signal tests." Thanks to Kendrick and Ben having saved copies of the reports describing the testing process, a good deal more of this interesting tale can now be told.