The flashing rear-end device, or "FRED," (also called an end-of-train device, ETD or EOT) is an electronic device mounted on the end of freight trains in lieu of a caboose. They are divided into two categories: 'dumb' units which only provide a visible indication of the rear of the train with a flashing red taillight; and 'smart' units which also send back data to the crew in the locomotive via telemetry.[1] They originated in North America, and are used elsewhere in the world.
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The 'smart' FRED devices monitor functions such as brake line pressure and accidental separation of the train using a motion sensor, functions that were previously monitored by a crew in the caboose.[1] The FRED transmits the data via a telemetry link to the Head-of-Train Device (HTD) in the locomotive, known colloquially among railroaders as a 'Wilma'. This is a play on the first name of the wife of cartoon character Fred Flintstone. In Canada, this device is known as an SBU (Sense and Braking Unit).
A typical HTD contains several lights indicating telemetry status and rear end movement, along with a digital readout of the brake pipe pressure from the FRED. It also contains a toggle switch used to initiate an emergency brake application from the rear end. In modern locomotives, the HTD is built into the locomotive's computer system, and the data is displayed on the engineer's computer screen.
Railroads have strict government-approved air brake testing procedures for various circumstances when asembling trains or switching out cars en route. After a cut is made between cars in a train and the train is rejoined, in addition to other tests, the crew must verify that the brakes apply and release on the rear car (to ensure that all of the brake hoses are connected and the angle cocks, or valves, are opened). In most cases, the engineer is able to use data from the FRED to verify that the air pressure reduces and increases at the rear of the train accordingly, indicating that proper brake pipe continuity. This device is said to constitute a fail-safe condition.
The FRED reduced labor costs, as well as the costs of the purchase and upkeep of cabooses. The Brotherhood of Conductors, and Brotherhood of Railroad Brakemen were also greatly affected by FRED, as this electronic unit replaced two crewmen per train. The widespread use of FREDs has made the caboose nearly obsolete. Some roads still use cabooses where the train must be backed up, on short local runs,[1] as rolling railroad police stations and transportation for right-of-way maintenance crews.
The first FRED use is attributed to Florida East Coast Railway in 1969, soon other Class I railroads began using FREDs as well, until the mid 1980s when they were common equipment.[1] Early models were little more than a brake line connection, battery and flashing tail light. As their use became more widespread through the 1980s, FREDs were equipped with radio transmitters to send brake pressure data to a receiver in the locomotive. To reduce the cost of battery replacements, ambient light sensors were added so the flashing light on the FRED would illuminate only after dark. Later models have a small turbine-powered electrical generator using air pressure from the brake line to power the FRED's radio and sensors.
The one-way communication of brake data from the FRED to the locomotive evolved into two-way communication that enables the engineer to apply the brakes from both ends of the train simultaneously in an emergency.[1] This is useful in the event that a blockage in the train's brake pipe is preventing all of the cars in the train from going into an emergency application. Such a situation could be dangerous, as stopping distance increases with fewer functional brakes. Dumping the brake pipe pressure from both the front and rear of the train ensures that the entire train applies its brakes in emergency. Other electronics within the FRED were also enhanced, and many now include GPS receivers as well as the two-way radio communications.
Railfans and railway photographers sometimes monitor FREDs as early warning systems to detect approaching trains. FREDs in North America operate on the 452.9375/457.9375 MHz frequency pair with the exception of those operated by Norfolk Southern Railway, which uses AAR channel 67 (161.115 MHz).[1] Railfans often program these frequencies into their radio scanners, which can provide a handy indicator of train activity (usually 2–5 miles, transmitting at 2 watts).
In Australia a number of safeworking systems require end-of-train devices on trains. They vary from simple flashing lights with no air brake connection, to complete End of Train Air System (ETAS) or Sense and Brake Unit (SBU) devices.[2][3]