Axle Counters

Axle Counters – Track Vacancy Detection: Overview

The reliability of an Axle Counter System is imperative in order to keep the network running safely and efficiently. An Axle Counter System determines the track vacancy; it supplies the information about whether a track in a particular section is clear or occupied, thereby permitting safe, trouble-free and efficient operations management of trains. Track vacancy detection is indispensable for safe rail operations and is a deciding contributor to trouble-free rail operations.

Siemens Mobility’s Axle Counter System can be used in a variety of applications: 

  • Main and branch lines, station areas, point areas
  • Single- and multiple-track lines
  • Lines with and without blocks
  • All types of traction
  • All common rolling stock types
  • Track sections of any length
  • Train speeds up to 450 km/h (250 mph) 

    There are a variety of components that create Siemens Mobility’s Axle Counter System, some are trackside which communicate with the indoor equipment which is housed in a relocatable equipment building (REB) or modular equipment housing (MEH):

Trackside equipment  

  • ZP 43 electronic wheel detection equipment
  • DEK wheel detector (transmitter/receiver)
  • Signalling cable between the cable distributor and the axle counter module

Indoor equipment

  • Axle counter module with ID plug
  • Connecting cables between ACM 200 or ACM 250 and the cable termination rack/cabinet 
  • Switch
  • Power supply module
Siemens Mobility Clearguard ACM 200 & 250 Axle Counter

Reliable and Cost-Effective Track Vacancy Detection

Siemens Mobility’s Axle Counter System is proven, SIL 4 technology with installations in 18 countries, using over 4,000 ACM Axle Counter modules.

For use in local transportation links within urban areas as well as for mainline, Siemens Mobility has developed a generation of smart track vacancy detection systems that offer benefits that have not been seen before in signalling.

The systems configuration is based on an Ethernet network where the ACM 200 & 250 use intercommunicating modules for a more reliable communication stream. The ACM 200 & 250 Modules evaluate the signal pulses that are transmitted by the wheel detection components by comparing the number of axles entering the track vacancy detection area, with the number of axles leaving it. The ACM 250 (only) can monitor 2 track sections simultaneously.

The ACM 200 & 250 modules are very quick to install which aids commissioning time constraints and cuts installing costs as the robust metal housing can be installed by simply locking it into position on a mounting rail.  Further connection benefits are realised as the modules are connectable to new and existing interlockings of any type of subsystem which reduce rail closures as it is quicker and easier to connect to existing interlocking systems.

The interface is very intuitive with data configuration being completed via a graphical user interface on an integrated website within the module. This ensures that installation and maintenance procedures have optimal support and can be completed quickly and efficiently, causing minimal disruption to the passenger.


Additional mitigation of passenger disruption is provided as the hardware replacement and extension or configuration updates can be carried out whilst powered with no system interruption, and within a short space of time. The modular system architecture allows the installation to be upgraded or extended for future projects where both ACM 200 & ACM 250 are compatible. The ACM 250 (only) uses WNC+ which is compatible with the Trackguard WESTLOCK and Trackguard WESTRACE interlocking families.


Maximum operational efficiency is created as each module has its own IP address and can therefore be integrated into redundant network systems; subsequently in case of connection failure, communication between module and operation control system is still possible.

Siemens Mobility Clearguard ZP D 43 Electronic Wheel Detection Equipment

The Clearguard ZP D 43 (ZP D 43) is easily mounted trackside and communicates with the ACM 200 & 250 modules to determine track vacancy.


The variation of UK weather conditions does not create reliability or safety issues as the flexible working temperatures allow the ZP D 43 to operate in snowy, humid or flooding conditions at ambient temperatures from -40 ◦C - 80◦C. This reduces the amount of maintenance call outs as Siemens Mobility's durable Axle Counting system will continue to operate when other systems fail due to adverse weather conditions.


For a smooth installation process the ZP D 43 is compatible with all common rail profiles and with the robust case, debris and environmental characteristics pose little threat to the reliability of detection. When maintenance work is being conducted, metal interference such as steel toe caps do not affect the performance of the machine. The convenient calibration process is strengthened via the automatic calibration indication LEDs which significantly speeds up installation times and results in significant cost savings.

Further Information

To learn more about the Clearguard ZP D43 system, download the datasheet