>>1571704>>1571725>>1571749>>1571769Trams are just street running (or at-grade ROW) light railways. Rail buses are the predecessors to modern-day light railways, which may be moder purpose-built LRTs, older, "1st gen" LRTs from the early 20th century (may have been interurban-type, local regional railways, etc.), or re-purposed heavy rail lines which lost their heavy traffic and were converted to low-traffic lines.
The Dietikon-Bremgarten railway in Switzerland is an example of a 1st gen LRT, originally an electric interurban-type railway which still works as such albeit modernized, but using vehicles not much larger than a bus (though they get coupled into pairs during rush hour)
The Lleida-La Pobla de Segur is an example of a former heavy rail line. It was intended as a line across the Pyrenees, but never completed, so it didn't get the heavy traffic it was conceived for. For a time actual rail buses ran on the line, now modern LRT-type diesel vehicles also not much larger than a bus run there.
Mostly, the railbus design isn't considered practical anymore, and compact articulated LRT units are preferrable. But they have about the same function as the old rail buses, to offer a cheap, compact rail vehicle that's economical to run on low-traffic lines.
