High-speed trains, conventional-speed passenger trains, urban railways, and tramways often operate independently with distinct boundaries.

When it comes to Germans, the predominant impressions are often of being precise, meticulous, earnest, and thorough, among other traits.

If one word were to summarize, it would be "rigorous." However, the rigorous nature of Germans sometimes leads them to operate on separate tracks. While it might be understandable to have high-speed trains, conventional trains, and urban railways operating on the same track within a high-volume railway passenger system, why would tramways, a medium-capacity mode of rail transport, join the fray?

In the early 20th century, Germany witnessed the phenomenon of mixed operation of tramways and railway trains. For instance, between the cities of Cologne and Bonn in North Rhine-Westphalia, trains seamlessly traversed between railway tracks and tramway tracks to ensure smooth operations between urban and suburban areas. People overcame significant differences between tramways and railway trains during construction and operation.

The first modern mixed-operation rail line also appeared in Germany. In the autumn of 1992, tramway vehicles traveled from the tramway network in Karlsruhe's urban area onto railway tracks leading to the town of Bretten. This modern urban rail transit system now has an internationally recognized name: "Tram-Train."

Tram-Trains are vehicles designed for mixed operation, running on tramway tracks in city centers and on railway tracks in suburbs and satellite cities. Tram-Trains seamlessly combine existing railway lines with newly built tramway lines, improving the efficiency of existing rail facilities.

Tram-Trains must meet both tramway construction and operation standards as well as railway operation standards.

So, how did Germans overcome the significant differences between tramways and railway trains to enable vehicles to run seamlessly between tramways and railway tracks?

Although tramway and railway tracks have the same gauge (1435mm), the tracks used are significantly different. Tram-Train wheels are a fusion of tramway and railway train wheels, designed with a wheel profile that allows operation on both types of tracks.

2. Clearance Restrictions:

German regulations specify that tramways have a maximum allowable width of 2.65m, while tram-trains and passenger trains have maximum widths of 3.15m and 2.90m, respectively.

This clearance issue mainly arises at platforms, where direct docking of tramways at railway platforms would result in a gap too large for passengers to easily embark and disembark.

3. Power Supply Systems:

Tramways generally use 600-750V DC power, suitable for safe operation within urban areas.

On the other hand, railway trains typically use high-voltage AC power (15kV/16.5Hz). To adapt to these differing power supply modes, a dual-power supply tramway vehicle was introduced in Karlsruhe in 1991. This vehicle operates on 750V DC power on tramway lines and 15kV high-voltage AC power on railway sections, a solution known as the "Karlsruhe model."

With increasing demand for public transportation, various innovative rail transit modes have emerged, and the Tram-Train model is increasingly embraced by governments and people worldwide. Metropolises with millions of inhabitants often experience significant passenger flows, whereas standalone tramways and subways can achieve greater practical value.