Szeged Transport Company (SZKT) is a key local public transport operator specializing in electric transport (tramway and trolleybus) in the city of Szeged, Hungary. SZKT operates 44 trams, 60 trolleybuses, and 10 diesel buses (the latter for replacement service) as well as infrastructure comprising 36 km of tram tracks, 37 km trolleybus catenary, 10 power substations, and 2 depots.

In addition to its daily operations staff, SZKT has its own technical department specializing in capital reconstructions, as well as tram and trolleybus refurbishments and modernizations.

With a strong emphasis on extending their assets lifecycles and reducing waste as well decades of recycling practices both for infrastructure elements as well as vehicles, SZKT is actively engaged in innovative circular economy initiatives within the CE4CE Interreg Central Europe project. One of the company's primary objectives is to optimize the circulation of materials, equipment and components within their fleets.

In their 44 units tram fleet Szeged operates as many as 35 Tatra trams of various types (KT4D-M, KT4D-ME, T6A2H, B6A2-ME), which were produced between 1985-1997. While these trams remain operational, their longevity depends on maintenance and spare parts availability. With proper upkeep and spare parts supplies the operation lifetime of these vehicles can be extended for further decades, as it is the practice of many Czech, Hungarian, Polish and other central and eastern European cities, which still operate Tatra trams. The biggest hurdle though is the supply of spare parts. Mechanical parts are relatively possible to be produced as replacements by several companies, however electronic parts (especially digital units) are particularly challenging since they are producer-specific, and the know-how is often not available for outsiders. They are not generic off-the-shelf parts; rather, they are intricately tied to the specific tram models and their proprietary systems.

The supply of door opening and closing mechanism on Tatra T6A2 and KT4D-ME trams is a particular problem since these regulation units are not in production anymore. SZKT has these on 15 KT4D-M/KT4D-ME trams (4 doors/vehicle) as well as on 13 T6A2 units (3 doors/vehicle). Altogether there are 99 units, and the issue is that there are no spare parts available on the market. In case of a malfunction Szeged must either repair it in-house yet this procedure is not indefinite, or - in the worst-case scenario - take these vehicles out of operation as tram door control units are critical for passenger safety and efficient tram operation. Without functional door regulation, trams cannot operate reliably, affecting public transportation services.

Szeged Transport Company found a solution to this problem by procuring a design and production of a prototype of a universal replacement hardware element for Tatra tram door units, along with new compatible control software that meets safety regulations.

Requirements for the prototype design were:

• - the door controller must be adaptable to various tram models and parameterizable with modern computer diagnostics;
• - thus, a new software must be developed;
• - the new part must be approved by the transport authority since it is a safety element.

SZKT managed to procure and develop a modernized, parameterizable tram door controller compatible with contemporary diagnostic tools. A mass production of a developed prototype is expected by Q3 2025 in order to replace the outdated control units in Tatra trams and save these vehicles from scrapping.

The technical and legal aspects of the new system will be addressed through rigorous safety testing and certification.

Thanks to this solution the primary goal achieved is the extension of the lifecycle of Szeged's tram fleet by introducing adaptable, industry-standard components that prevent premature tram decommissioning due to spare parts shortages. The extension of operational lifespan of tram door systems is estimated to be by next 10-15 years, preventing unnecessary vehicle replacements and reducing waste.

This solution is scalable to other tram operators in search of this part as the developed design for the tram door control unit prototype is universal and can be easily deployed by other public transport companies.

The pilot described  aligns with the city of Szeged's E-Mobility Concept (approved in 2023), which emphasizes the necessity of introducing sustainability and circular economy principles into their public transport.