Primary Train Detection for Mainline Signaling

A key component of train safety and on-time performance for mainlines is a reliable primary train detection system. There are several types of signaling technologies that can be used for primary train detection, such as track circuits, presence detection (PD) loops, and axle counters. 

Each of these systems operates under measurably different principles, and vary widely in their technical features, reliability, and resilience. Furthermore, design complexity, as well as installation and maintenance costs, may differ significantly within each technology category.

Challenges of conventional train detection systems

Expensive and difficult installation


Most of the technologies used for primary train detection involve expensive, time consuming and often difficult installation, leading to increased costs. Track circuits require drilling of the rail, and may require joints, bonds, filters, and wiring for each unit. Presence detection loops must be laid out in a specific manner, requiring complex system design and tedious installation.

Frauscher Benefits

Simple installation and seamless integration

Frauscher wheel sensors are installed within minutes, simply clamped to the rail using the Frauscher rail claw. Our axle counting systems can seamlessly integrate with any existing train detection system. Ethernet protocols and discrete outputs ensure that new and legacy systems can be interfaced with the Frauscher system. The existing system continues to function during installation and overlay, as well as throughout the testing period. Once testing is complete, there is a smooth cutover to the axle counting system. In addition, proper positioning of wheel sensors within crossovers eliminates the dead areas that can exist with other systems.

Complex electrical design required


Depending on the type of track circuit being used, parameters such as electrical isolation, filtering of current and operating frequency must be managed. This is especially true for switches and crossovers where several different circuits may interact with one another. Presence detection loops require stick logic to ensure certain track sections are clear.

Frauscher Benefits

No complex electrical design required

Frauscher wheel sensors work on an inductive principle, and are simply clamped to the rail without direct electrical rail contact. No changes to the existing rail structure or electric circuitry are required. This can be of particular benefit in areas with crossovers and switches, where several different circuits could interact. The absence of trackside electronics contributes significantly to the robustness of the system.


Downtime issues during severe weather or temperatures


Reduced availability during severe weather or extreme temperatures can be an issue with track circuits and presence detection loops commonly used for primary train detection. Environmental conditions frequently cause shunting issues for track circuits, and can also have adverse effects on the reliability of PD loops, since by design they are constantly exposed to the elements. Significant system delays and potential safety issues can result from the compromised availability of track circuits and PD loops.

Frauscher Benefits

Unaffected by harsh environment or extreme temperatures

Frauscher wheel sensors are not affected by common environmental and track conditions that can negatively impact the functionality of track circuit systems and PD loops. Flooding, snow, ice, salting and leaf accumulation, as well rusty rails or other track and ballast issues, will not affect uptime or availability.  

Limited track section length


Due to track section length limitations of conventional systems, additional and costly equipment and installation efforts are required to safely cover longer distances. Examples include areas where stations are located several miles apart, or grade crossings with longer approaches. These additional expenses can put an added strain on already tight budgets, making some systems economically infeasible.

Frauscher Benefits

Unlimited track section length and flexible design

Frauscher axle counting systems offer unlimited track section lengths, a capability that requires less equipment to be purchased, installed and maintained. The flexibility of a decentralized architecture allows wayside huts, installed close to the sensors, to be connected via Ethernet. This provides maximum flexibility in system design while keeping cable runs short.

Frequent and costly maintenance requirements


Maintenance work required with conventional systems must be completed during off times, which involves higher labor rates. Significant costs will be incurred over a track circuit’s lifetime to maintain bonds, joints, and wiring, requiring frequent onsite inspections and repairs. Similarly, presence detection loops are laid out on the ties and openly exposed to the elements, which may require frequent maintenance to rectify issues resulting from this exposure. In both instances, the additional cost and downtime required to conduct this maintenance also involves more time on track for crews, negatively impacting worker safety.

Frauscher Benefits

Reduced maintenance requirements and costs

Frauscher wheel sensors provide low maintenance and overall lifecycle costs compared to track circuits, PD loops and other axle counter systems. Maintenance is required just once every two years, and involves a simple visual and functional inspection that takes just minutes per sensor. This minimizes the need for worker track access to perform maintenance checks, improving worker safety.

Remote maintenance and diagnostic capabilities

The Frauscher Diagnostic System FDS and Remote Monitoring Display RMD provide remote access to system operation and predictive maintenance information from all outdoor equipment locations. This remote access capability allows the operator to troubleshoot the system from their operations center. Preventive and targeted maintenance can then be performed, often remotely, minimizing the need to place work crews on track for periodic resets and maintenance.

Issues with electric traction systems


Electric traction systems often complicate the utilization of track circuits. Sophisticated audio frequency track circuits are required, and consideration of electric isolation and frequency management is necessary during installation, which is difficult. Although presence detection loops are negatively affected by EMI to a lesser extent than track circuits, performance and availability issues are still possible when using this technology.

Frauscher Benefits

Compatible with electric traction systems

Frauscher axle counting systems are fully compatible with electric traction systems, which is not the case with standard train detection systems. The installation of sophisticated audio frequency track circuits that are required to avoid EMI issues requires adjustments to track infrastructure, since the AF track circuits require bonds, joints, wiring and isolation for installation.

Frauscher axle counters do not require modifications to track infrastructure, as they are simply clamped to the rail without drilling, and are virtually immune to traction return currents. This allows operators to use the same signaling solution throughout their network.


Frauscher axle counters and wheel sensors provide a wide range of solutions for primary train detection. Compared to the conventional systems that are often used, Frauscher systems increase safety and availability with significantly lower installation and life cycle costs.

Our waterproof (IP68 rated) wheel sensors are highly reliable, even in harsh environmental conditions. Installation of a Frauscher axle counting system does not require modifications to existing track structure, and it can interface in a vital manner with the operator’s existing system.

Frauscher systems require preventative maintenance just once every two years, which significantly reduces man hour requirements and costs for the operator. Advanced tools such as the Frauscher Diagnostic System FDS support remote diagnostics and data logging. Overall maintenance and life cycle costs can be further reduced by allowing many checks to be handled remotely from the central station.

Frauscher wheel sensors and fail-safe axle counting systems offer unparalleled performance, providing reliable and cost-effective solutions for primary train detection.