Minh Nguyen
Light rail is an infamously ill-defined mode of transportation, but Muni Metro is instantly recognizable as an example of it.

Elsewhere in the Bay Area, there are street-running segments of heavy rail in both Oakland and San José. (In fact, Oakland is world-famous for it thanks to Jack London.) Judging from https://en.wikipedia.org/wiki/Street_running_train#United_States, street running is a largely North American phenomenon these days.

Light rail, streetcars, and heavy rail are distinguished not only by their vehicle types but also by their operating rules. If any of these railways were tagged as tram lines, in whole or in part, it would be deeply surprising to both mappers and data consumers and would possibly lead to real-world safety issues. Some extra quests to affirm the absence of crossing gates doesn’t seem like a major problem at all. After all, there are plenty – plenty – of heavy rail crossings without gates too.