UPDATE February 2016: While this post’s deep dive is valid enough, I would no longer agree with my past self that exclusivity of right of way is secondary in defining the difference between streetcars and light rail. I no longer agree with this post’s claim that exclusive right of way is more important for longer transit trips than for short ones. It is always a crucial driver of reliability, and its absence continues to be the defining features of what most Americans call “streetcars” as opposed to light rail.
The dividing line between what Americans reference as a streetcar and what they call light rail is not nearly as defined as one might assume considering the frequent use of the two terminologies in opposition. According to popular understanding, streetcars share their rights-of-way with automobiles and light rail has its own, reserved right-of-way.
But the truth is that the two modes use very similar vehicles and their corridors frequently fall somewhere between the respective stereotypes of each technology. Even the prototypical U.S. light rail project — the Portland MAX — includes significant track segments downtown in which its corridor is hardly separated from that of the automobiles nearby. And that city’s similarly pioneering streetcar includes several segments completely separated from the street.