Translations:Semafory samoczynne (SBL)/1/en

There are three types of SBL in use on polish railways, these are: two-state, three-state and four-state. Automatic signals are controlled by passage of trains and track circuits. SBL signals can be identified by white mast.

Two-state automatic signals

Two-state signals have a two light head comprised of a red and green light mounted on it. This type of signal is preceded by distant signal placed in braking distance.

Three-state automatic signals

Three-state signals have a three light head comprised of green, red and yellow light mounted on it. This type of signal also works as a distant signal informing the driver about the aspect of next signal. These signals are placed in braking distance between one another. This type of automatic signal is the most common type of automatic signal

four-state automatic signals

Four-state signals are comprised of same lights as three-state signals, the difference lies in the fact, that this type of signal can display a S3 aspect. This aspect informs the driver that two blocks in front of the train are free, and depending of where the signal is, driver might have to reduce the speed to 100 km/h at next signal. Thanks to use of this signal distance between signals can be reduced to half of the braking distance for this line. This type of automatic signal is usually used on high speed lines.