LS (stands for “Liniový Systém” in Czech, “continuous system” in English) is a

cab signalling Cab signaling is a railway safety system that communicates track status and condition information to the cab, crew compartment or driver's compartment of a locomotive, railcar or multiple unit. The information is continually updated giving an ...

and a

train protection system A train protection system is a railway technical installation to ensure safe operation in the event of human error. Development Train stops The earliest systems were train stops, as still used by the New York City Subway, the Toronto subway, t ...

used on the main lines of the Czech and Slovak railways (on all lines which track speed exceeds 100 km/h in the Czech republic or 120 km/h in Slovakia). This system continuously transmits and shows a signal aspect of the next main

signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...

in driver's cabin and when the driver's activity is needed (e.g. a speed reduction), it periodically checks the driver's vigilance (he has to press the “vigilance” button; else the emergency brake is applied). This is the main function of on-board part of the LS-system (continuous cab signalling and checking the driver's vigilance when needed). Trackside part of the LS-system is based on coded

track circuits A track circuit is an electrical device used to prove the absence of a train on rail tracks to signallers and control relevant signals. An alternative to track circuits are axle counters. Principles and operation The basic principle behind t ...

using

carrier frequency In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has a m ...

75 Hz with 100%

amplitude modulation Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the amplitude (signal strength) of the wave is varied in proportion to ...

( on-off keying). The signal aspect of the next signal is coded in modulation frequency (there are used four modulation frequencies: 0.9 Hz – 1.8 Hz – 3.6 Hz – 5.4 Hz; it means that it is possible to transmit four signal aspects). The LS-system can transmit these signal aspects: * Red aspect – train must stop at the next signal. * Aspect requiring decreasing of train's speed – train must reduce its speed at the next signal to the value shown at the lineside signal. * Yellow aspect – there are no speed restrictions at the next signal, but the subsequent signal is red. * Green aspect – there are no speed restrictions at the next signal. Ls90 zobrazovac

The trackside part of the LS-system became an integral part of every Automatic Block used on the lines in the

Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...

and in

Slovakia Slovakia (; sk, Slovensko ), officially the Slovak Republic ( sk, Slovenská republika, links=no ), is a landlocked country in Central Europe. It is bordered by Poland to the north, Ukraine to the east, Hungary to the south, Austria to the s ...

. Almost the entire fleet of locomotives is equipped with the on-board part of the LS-system (in one of these versions: LS II–IV, LS 90, LS 06 or MIREL VZ1).

Mirel VZ1

The on-board device Mirel VZ1, unlike older devices, generates a braking curve according to a received restrictive signal. Nevertheless, the trackside part of the LS-system offers too little information to generate a usable braking curve. Thus, this braking curve is so restrictive that its use is questionable. The driver has two choices then. He has to regulate the speed so that it is lower than the generated speed, otherwise emergency braking is applied; or he can use manual mode and there is no braking curve (only checking the driver's vigilance). However, the Mirel VZ1 has an optional ability to decode the Hungarian signals of the EVM 120. Therefore, the newest Škoda locomotive 380/381 (they will be operated also in Hungary) were equipped with Mirel VZ1 instead of LS90 board unit. Railway signaling in the Czech Republic Railway signaling in Slovakia Train protection systems