What's the difference between an LRV and an HRV?

[Quixote]

Most of us know that heavy rail transit (HRT) is about capacity, grade-separation, frequency, and electrification, as opposed to the type of rolling stock used. Yet, many of the world's rapid transit systems have rolling stock with characteristics commonly associated with light rail — articulation (for flexibility) and electrification via pantographs — but are still considered electric multiple units (EMUs) as opposed to light rail vehicles (LRVs).

There are two or three systems in the world that utilize what would be considered LRVs, but otherwise have all the operational characteristics of an HRT system and are considered "metros." These include Manila's LRT Line 1 and MRT Line 3, the Vienna U-Bahn's U6, and perhaps London's Dockland's Light Railway (DLR). The DLR originally utilized the same rolling stock as a tram in Essen, Germany (only powered by third rail), but now uses what are considered "single-articulated EMUs," according to Wikipedia.

So what makes something like this...


https://www.metromadrid.es/en/rolling-stock

... a heavy rail vehicle / EMU technologically and/or mechanically different than something like this? Is there equipment above and below HRVs/EMUs that make them fundamentally distinct from LRVs?


https://www.google.com/search?q=mani...19jni3kFMCZ4cM

Manila MRT:

• Video Link

• Video Link

Vienna U-Bahn U6:

• Video Link

[Quixote]

Here's a 5-car LRV consist in Edmonton, probably 450 feet long. If this line featured no grade-crossings, would this not qualify as heavy rail or a "metro"? Plenty of rapid transit lines run at-grade and many don't run trains of this length.

• Video Link

[homebucket]

Growing up in SF and riding transit for many years, the distinction is pretty clear in terms of both rolling stock and operational characteristics.

BART = heavy rail/regional. Muni Metro = light rail/local.

BART is fully grade separated, powered by third rail, faster (top speed of 80 mph) and smoother, and has much higher capacity with up to 10 car trains, and functions as a rapid transit/commuter rail hybrid.

Muni Metro is light rail, powered by overhead lines, and it's much slower (top speed of 50 mph) and feels less refined. Start/stops can be somewhat jerky. And in much of the city functions as more of a streetcar, which is one of its and many other light rail system's primary disadvantages, giving it a much slower average speed, especially if there's not optimized signal priority. It's also lower capacity with 2 car trains.

[homebucket]

PC: homebucket

[Quixote]

Operationally, the difference is clear.

What I want to know is if there's a fundamental, anatomical difference between HRVs that run on pantographs and LRVs that function as part of a rapid transit system.

[Nouvellecosse]

There are characteristics associated with one or the other but like most things it's possible to have examples that combine characteristics of both. Like how there used to be cars and trucks, but over time there were things like the El Camino, SUVs, vans, minivans, and now crossovers. They all have some characteristics of both. But many have enough characteristics of one side or the other to still be characterized as such. And even if most vehicles were crossovers that couldn't be classified as more one than the other, conventional cars and trucks still exist allowing the terms to retain some utility.

The question of how to classify and categorize things is central to the philosophical field of ontology (a subset of metaphysics). It aims to establish identities in terms of properties that one can use to identify things and distinguish different things from one another. An identity usually constitutes one or more necessary properties and some have one or more necessary and sufficient properties. For instance, it is necessary for a body of water to contain H20. But that condition isn't sufficient since there are many things that contain H20 that aren't bodies of water. Potting soil, a butterfly, a cactus, etc. You'd need a longer list of necessary conditions. But bodies of water which meet all the necessary conditions will still have other properties that aren't necessary. Some will be frozen part of the year and others won't. Some will have certain dissolved particles that others lack, etc.

At times you'll also encounter things that don't have any necessary conditions. They qualify as a particular thing simply by meeting a sufficient number of optional conditions. For instance, there are many types of boats. One might say that for something to be a boat, it must float (necessary condition). But clearly this isn't a sufficient condition since lots of things can float (ducks, beach balls, lily pads, etc.) And most would agree that if a boat sinks (poorly designed or capsized by a wave) it's still a boat. Perhaps is must designed with the intention that it will float. But if a craftsman designed and built one as a hobby with the intention of putting it on display in his backyard and never using it on water, most people would still recognize it as a boat and call it such. When an identity is based on having a sufficient number of optional conditions but no strictly necessary conditions, it's referred to as a family resemblance identity. There may be no single trait (property) that they all share, but they're still recognizable as part of the same related group. I think this is the case here. Some trains are recognizable as LRVs even if there's no one specific property that you can point to that all other LRVs have and no metro train has.

There are some things whose properties are so clearly and inherently distinct that there's no question or leeway in how they're classified. These are referred to as "natural kinds". There's no overlap in properties between it and other natural kinds. But for the vast majority of things, how they're classified is simply up to people to choose which properties to group together and to consider important. For cars and trucks, things like what colour they are, whether they use diesel, gasoline, or electric propulsion, or country of origin aren't relevant to which category we place them in. But things like unibody vs body on frame design, ground clearance, and towing capacity are important. That's because identities are generally about function. When you're trying to classify something as one type of thing vs another, the leading question is what you're trying to achieve? Trucks are better than cars at some things and vice versa. Metro trains are better than LRVs at some things and vice versa. And sometimes you want some some combination of these qualities. Usually you can look at a transit line and get a pretty good sense of why a particular rolling stock was chosen. So when you say "operationally the difference is clear" I think you answered your own question. Clearly neither are natural kinds nor do they have a distinct set of necessary and sufficient conditions other than those shared by rail transit vehicles in general.

[JManc]

@ homebucket. That bottom pic over by Soma?

[homebucket]

Originally Posted by JManc

@ homebucket. That bottom pic over by Soma?

Yup. That’s a shot of SoMa, looking up 2nd St, from the View Level (upper deck) concourse at Oracle Park.