The Antiplanner has been reading lots of rail transit plans lately and it strikes me that the standard jargon for different kinds of rail systems is confusing. Most people think that the terms “light” and “heavy” rail refer somehow to weight, when they don’t. By extension, if trains look heavy, they must be heavy rail.
This results in the most confusion between heavy rail and commuter rail. Both use the same weight of rails, so lots of people call commuter rail “heavy rail.” In fact, weight has nothing to do with it–most light-rail lines are built with the same weight of rails as heavy-rail lines.
As the Antiplanner has noted before, the terms “light” and “heavy” really refer to carrying capacity. Light rail is short for “light-capacity” rail while heavy rail is short for “heavy-capacity” rail. The confusion results because the term “heavy” is rarely used to mean “high” while “light” is rarely used to mean “low.”
