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.”

So I modestly suggest we use a different terminology. Instead of “heavy rail,” we should say “high-capacity rail.” This would include subways and elevated, any trains that operate exclusively in their own right of way and whose potential length is eight cars or greater.

This means the term “low-capacity rail” should be used in place of light rail. While high-capacity rail has trains of eight or more cars, low-capacity rail has trains of just two to four cars, depending on the length of the blocks on the city where the trains are to run.

By extension, streetcars are “ultra-low capacity rail.” Unlike low-capacity rail, streetcars are not designed to be coupled together and so run only one car at at time. This, combined with the fact that each car is no more than two-thirds as long as a low-capacity railcar, means that a streetcar line has a third or less the capacity of low-capacity rail transit.

Commuter trains generally operate only during rush hours and often share tracks with freight trains, which use them during other hours. Unlike high- and low-capacity rail, which is usually electrically powered, commuter trains usually consist of a Diesel locomotive pulling two or more passenger cars.

But more confusion results because some cities have started what they call commuter-rail services that consist of one or two self-powered cars that often operate half-hourly all day long, and quarter-hourly during peak hours. The Federal Transit Administration has recently decided to call this type of service “hybrid rail” because it is something like a cross between commuter rail and low-capacity rail.

Instead, I propose to call commuter trains that consist of a locomotive and cars “moderate-capacity commuter rail,” while the hybrid rail should be called “low-capacity commuter rail.”

Is there such a thing as high-capacity commuter rail? Probably not, but ordinary commuter rail should be called “moderate-capacity” because its capacity falls well short of high-capacity rail. Even the most frequent commuter trains rarely operate more than five times per hour, which can’t compare with high-capacity rail which can operate at least twenty times an hour.

Rail advocates won’t like this nomenclature because they want to give people the misleading impression that light rail and even streetcars are high-capacity transit. That’s why the change is all the more urgent so that people can really understand what they are getting when their politicians decide to spend a billion dollars or more on a low-capacity rail line.

So from now on, this blog will use these terms: high-capacity rail; low-capacity rail; ultra-low-capacity rail; moderate-capacity commuter rail; and low-capacity commuter rail. I suggest others do the same.