Making Subways Safer with Versatile, Reliable Interconnects

By Tarak Viol | February 18, 2025

Fire protection systems in 27 underground rail stations are currently being updated. Fieldbus couplers and I/O modules from the WAGO-I/O-SYSTEM 750 and 753 are playing an important part.

Passenger safety is the central focus for the Frankfurt Transportation Authority (VGF – Verkehrsgesellschaft Frankfurt). This mission extends from the public transportation lines to points along the system, including stations where passengers board and disembark. Enhancing fire safety is a key part of this initiative. The fire protection systems in the 27 underground stations that comprise the Frankfort network are currently being completely overhauled. As the city’s public transportation provider, VGF operates a total of nine subway and ten streetcar lines. Around 350 rail vehicles are in service practically around the clock to transport over 160 million passengers annually.

Fieldbus couplers and I/O modules from the WAGO-I/O-SYSTEM 750 and 753 are playing an important part in safety upgrades being made to the Frankfurt lines.

System upgrades enhance fire protection

Among the 86 stations associated with the city’s rail network, 27 are completely underground. This is where fire protection plays an important role, as it does in all buildings where people gather. It must be possible to rapidly evacuate the stations in case of emergency. The VGF fundamentally revised its fire protection systems design for underground stations. An analysis of fire protection incident reports, combined with the integration of the building control system formed the basic of the new design concept. The fire alarm systems, which previously functioned autonomously, will now be linked into new systems that automate the building infrastructure across the individual stations.

Siclimat X building control system and SIMATIC-S7 controllers, both from Siemens, are used at the management level and automation level, respectively. In the new system, it is possible for the operators in the central control room to access all subsections in all stations, as well as most of the infrastructure systems. Within the subway stations, a redundant fiber-optic ETHERNET ring networks all the controllers with each other. The fieldbus connections to the individual subsections are implemented using PROFIBUS or PROFINET.

Connecting inputs and outputs at the PLC

The updated fire protection systems are now linked to the control room via a PLC. The fire alarm system consists of various fire protection elements within each station. In a dire scenario in which a train that is already on fire pulls into the station, an alarm must sound immediately to help passengers evacuate the station. A series of different actions need to be implemented simultaneously to make this occur, and these directives are stored on the PLC as an “in case of fire matrix.” These directives stop descending escalators, while elevators continue to the highest position and then hold. The ventilation system switches on, visual and acoustic signals prompt the passengers to leave the station, and smoke curtains separate various areas of the station in order to prevent the spread of smoke.

Several controllers are incorporated within each station for the individual subsections. In order to connect the inputs and outputs at multiple points, WAGO’s I/O system is used. PROFIBUS or PROFINET couplers are used, depending on the part of the control system in which the inputs and outputs are located. The WAGO components serve as data collectors, which detect signals and forward them to the responsible PLC. Even outputs are linked via the I/O system; for example, for controlling the voice alarm system. “By using WAGO’s I/O system, we have a suitable I/O module for practically any conceivable signal,” said Rainer Kuhn, who is responsible for converting the automation technology in the subway stations for the VGF.

Monitoring short circuits and cable breaks

In safety systems, the controller must be able to monitor signals with perfect reliability. “Before, we calculated a flow resistance and implemented a measurement via an analog input,” explains Kuhn. Now, by using “intruder alarm” modules from WAGO, this very expensive solution could be elegantly replaced by a single I/O system bus module. The 753-424 integrates monitoring for cable breaks and short circuits by default and easily assumes the monitoring of other inputs relevant to safety. “The intruder alarm module, which integrates all of these functions into a slender module, was one of the primary reason for choosing the WAGO-I/O-SYSTEM.”

Other advantages of the I/O system that appealed to the VGF include a modular design that ensures that a suitable I/O module can be retrofitted for any requirement. The 753 Series I/O modules that are being used in the subway stations have a pluggable connector, which makes installation and maintenance significantly easier. The technician removes the connector from the module, executes, for example, a measurement, and then reconnects the connector. Functionality is reestablished with only a few hand movements.

Kuhn says collaboration with the connector supplier helped the railways design and execute the updated safety system. “We profited greatly from the good advice we received from WAGO employees, especially while planning this system.”

Learn more about WAGO’s solutions for railway systems.