High axle loads, long train formations, and large transport volumes place a great deal of strain on the superstructure. This necessitates robust designs and maintenance strategies that make high levels of productivity possible. For Class I railroads, most of which are privately owned railway infrastructure companies, that is why the focus lies on maintenance productivity with minimal economic impact. The key is to maintain long sections of track in short track possessions while maximizing performance.

Against this backdrop, the ongoing development of maintenance methods is becoming increasingly important. The aim is to gain a data-driven understanding of the effectiveness of individual actions and to improve the stability of the track geometry in the long term while immediately increasing output.

Stable track geometry, maximum performance

Within the scope of our global research initiative, Plasser SmartTamping, we are investigating the tamping process and the resulting consolidation of the ballast bed. One sub-project focused on the specific requirements of heavy-haul railways in North America. In collaboration with Pennsylvania State University and a North American infrastructure manager, different squeezing times and the number of squeezing cycles were systematically varied on a main line operated by a Class I railroad. The progression of the track geometry was then monitored over an extended period, which made it possible to assess the long-term impact of the individual parameters.

A GRM3000 1-sleeper tamping machine, fitted with a complete sensor system, was used. Sensors in the ballast bed acted as smart ballast grains, providing real-time insights into the processes taking place within the ballast during and after the tamping process. This made it possible to quantify the impact of short squeezing times on the long-term progression of the track geometry.

The results clearly demonstrate the practical benefits: a more stable track geometry reduces maintenance requirements and extends the service life of the superstructure. At the same time, carefully selected tamping parameters make it possible to optimize squeezing times and maximize output without compromising quality. Short squeezing times temporarily increase output but have been shown to have a negative impact on the durability of the results.

This is where assistance systems such as Plasser TampingAssistant and Plasser TampingControl come into play. They assist with finding the ideal balance between productivity and quality.

Plasser TampingAssistant in use in the US

The specific operating conditions of North American heavy-haul railways place greater demands on machines and sensor technology, as was observed during an early adopter project for the Plasser TampingAssistant in the United States. Many tamping machines are equipped with only a single cab for driving and work, which means that the traditional sensor positions found on a front cab are no longer required.

The solution: move the sensor system to the front measuring trolley. The front measuring trolley is positioned in front of the main machine using either the short- or long-chord method. It serves as the front measuring point for the work chords and, thanks to its defined distance from the machine, provides a stable reference point for mounting the sensors. In order to train the Plasser TampingAssistant and make use of the production phase for the new tamping machines, the sensors were initially installed on a separate front trailer so that they could be operated independently of the tamping machine. The aim was to capture different turnout geometries and obstacles and to train the system to adapt to local conditions.

Following a training period of around eight months, the sensor system was integrated into a new 09-2X DYNACAT 2-sleeper tamping machine. In early 2025, this marked the first time that a turnout in a major North American rail freight network had been tamped autonomously.

GRM4000: an evolution of the GRM series for increased productivity

In addition to continuous-action multi-sleeper tamping machines, cyclic-action 1-sleeper tamping machines are also frequently used in North America. The advantage lies in their high flexibility: a low-loader or flat wagon can transport them quickly to the site, and they do not take up valuable track capacity time. For decades, tamping machines in Plasser American’s GRM series have proved themselves as a robust, versatile solution for plain-line tracks and turnouts. The split-head tamping unit combines a simple design with high adaptability, enabling a wide range of applications while excelling in terms of reliability.

The logical next step was to systematically refine the machine design. The successor model, the GRM4000, builds on the tried-and-tested components of the existing design, refining them specifically to deliver a higher output. The use of a newly developed 2-sleeper tamping unit makes it possible to significantly increase productivity once again without compromising transportability. The machine has been undergoing testing on open track since the end of 2025.

Thanks to TAMPLINK® technology, the GRM3000T’s performance has already been significantly enhanced: depending on requirements, a PTS90C can be coupled directly to the machine, or an additional trailer with a tamping unit can be used. Another step forward: digitalization of machine coupling. Where TAMPLINK® still required a mechanical connection, the Remote Stabilizer option enables wireless communication between the tamping machine and the track stabilizing vehicle. A PTS90C, controlled directly from the tamping machine, follows the lead vehicle autonomously without the need for additional personnel. Radar sensors continuously monitor the space between the vehicles, ensuring safe and efficient operation.