Tram-train systems use light rail vehicles but combine heavy rail running with on-street operation. Indeed this type of system enables tram vehicles to share railway tracks with conventional rail rolling stock but to also leave the rail network and run on-street in the same manner as a standard tram system. Tram-train systems have several significant advantages including a high passenger carrying capacity, potential for fast journey times and a high quality image. Tram-trains can be powered by electricity, diesel or a combination of both.

A further key advantage of tram-train systems is that they can provide increased penetration into the city centre by leaving the mainline railway lines and running on-street through the city centre area. As well as benefiting passengers this also helps to "free up" capacity at main line rail stations.

Examples:

• Bremen, Germany
• Saarbrucken, Germany
• Mulhouse, France (currently in development)