Monorail vs. light rail

This is in reply to a post in a newsgroup, however, the text is self-contained and does not require any knowledge of the previous discussion.

> Are there advantages unique to monorails?

There is one very narrow niche where it is advantageous.

Let's start with the basics. Generally, there are three possible types of alignment for a rapid transit system: underground, at grade, or elevated structure. "At grade" can be completely isolated, can be partially isolated (with grade crossings), and can be mixed with traffic (street running). In terms of the cost, the underground alignment is typically the most expensive, the elevated structure is the second most expensive, then goes "at grade completely separated", then "at grade partially isolated", and finally in many cases the cheapest is "street running".

Out of these three (or five) possible types of alignment the monorail is pretty much stuck to the elevated structure. In all the other cases, the monorail is so much more expensive than conventional rail modes, that there is no sense even discussing, for instance, "underground monorails". Conventional rail technology is far simpler and far cheaper to implement in all cases other than the elevated structure. (Why is monorail more expensive than conventional rail?)

However, even for the elevated structure monorail can be advantageous ONLY if the ENTIRE line is supposed to be elevated. This is the case when the development density is very high, such as in typical American downtowns. If the line needs to go somewhere else, there is a good chance it does not need to be elevated everywhere. Pretty much in any city in the U.S. outer areas are of considerably lower density, which can support at-grade running (for instance on some abandoned railroad right-of-way or on a highway median).

Now, if you have the need for an entirely elevated line within a high-density development, the advantage of the monorail is its relatively narrow elevated structure. Its cost is not substantially different from, say, a light-rail elevated structure, however, its size is smaller. This is generally touted as more "aesthetically pleasing". However, even this is changing, since modern safety requirements call for an evacuation cat-walk along the entire structure, that makes it comparable in width with any other two-track elevated structure.

So, as you can see, the niche is indeed very narrow, and that is the primary reason monorails are not implemented much. This is not conspiracy or anything, it is just the lack of consistent high density (in the U.S.), and, as a result, the lack of need for the entirely elevated lines.

> I have always enjoyed riding monorails as a kid. But I think given the
> cost and reliability of light-rail in the USA today vs. Monorail in the
> USA (e.g. the Las Vegas Monorail), light rail wins out.

The main advantage of the light rail and the main cause of its popularity in the U.S. is its VERSATILITY. Light rail can run on all five possible types of alignment, depending on the particular situation in a given area of a given city, such as: cost, density, station spacing, ridership, etc. Moreover, the same line can be running on one type of alignment in one area of the city and on another type of alignment in another area of the same city. The scenario very common in the U.S. is the following:

Outside of the downtown core, the density is extraordinarily low, and there is almost always a way to run a line at grade (e.g. on an abandoned railroad right-of-way or on a highway median), either isolated from traffic (no crossings) or partially isolated from traffic (with crossings). Some cases of street running in denser areas (San Francisco) are also known. But almost never an expensive option like a tunnel or an elevated stricture is needed for the entire outlying portion of the line (although some short viaducts or undercrossings are often used for the grade separation purposes).

In the downtown area, either underground alignment is chosen (St. Louis, Pittsburgh, San Francisco, Los Angeles, Philadelphia, Boston) or street running (Portland, San Diego, Sacramento, Minneapolis, Denver, Dallas, Houston, Baltimore). Occasionally, a railroad alignment can be available too (Cleveland). However, almost never there is a real need for an elevated structure. And if there were such a need, the same light rail could have been run on that structure too.

So, as you can see, light rail is just the perfect fit for the U.S. It works in all scenarios imaginable. Now, this is very different in Europe, where density is typically higher, and grade separation is almost always required. Thus, metros (grade separated systems) are often required. Street running or grade crossings are acceptable in much fewer cases. Even more denser are Asian cities, and there the choice is often limited to being between the underground and the elevated alignments. In many Asian cities fully elevated lines are well justified and indeed needed. However, coming back to the U.S., there is simply almost no appropriate densities here THROUGHOUT an entire line. Most large cities have already developed heavy rail (metro) systems, and most mid-size cities do not have enough density to justify anything more expensive than light rail with a lot of at-grade running.

> The inclusion of short tunnel segments or at-grade segments (with grade
> separation) does not make monorail noncompetitive in terms of cost
> relative to other grade separated systems.

The big assumption here is "short segments".  By and large, you are limited to the elevated structures: if most of your line is NOT elevated, monorail
has a big cost disadvantage.  The majority of realistic lines are NOT elevated 90% of the length, and thus monorail is indeed a noncompetitive mode for the majority of the realistic lines.

You see, if one REALLY wants, one can justify construction of an elevated line virtually in any place.  And then one can say, hey, why don't we build a monorail?  The point is that the task must be (and is) solved in a very different manner.  First you analyze different possible alignments (not modes yet!), and select the alignment that suits the particular situation the best.  And only THEN you select the mode that best fits to that alignment.  If your alignment has grade crossings, you typically build light rail.  If you alignment is completely grade separated but has elevated, underground and at-grade segments, you build the heavy rail (metro).  And ONLY IF the entire chosen alignment (or 90% of it) is elevated, there is some justification to consider monorail.

Often, monorail fans reverse the logic and FIRST choose the monorail, before a thorough analysis of the alignments and their advantages and disadvantages. However, this is not how this task should generally be approached. The choice of the alignment is always a much more major factor than the choice of the particular technical realization of the train that runs on that alignment.  From the practical point of view, the only thing the user (the city) is concerned is the alignment and the level of its isolation and its impact.  If there is any predisposition to a particular mode from the beginning, than it is not technically and economically justified.

> The advantages of full grade-separation are compelling.  Generally, the
> cheapest way to achieve grade-separation is by elevating a line.  Among
> elevated systems, monorail offers the least visual impact and the least
> noise impact.

There is a mistake in EVERY sentence in the quoted paragraph:

Yes, the advantages of full grade-separation are compelling.  But NO, the cheapest way to achieve grade-separation is NOT by elevating a line.  The cheapest way to achieve grade-separation is to use an at-grade alignment, such as a highway median or a railroad right-of-way. These alignments are frequently available in most American cities, and they are typically of substantially lower cost than the elevated structure.

Yes, among the elevated systems, monorail offers the least visual impact and the least noise impact.  However, elevated systems offer the MOST visual impact and the MOST noise impact out of all grade-separated systems.  Thus, if visual impact and noise impact are of great concern, you do NOT build an elevated system at all, be that monorail or bi-rail.  You build it underground.

So, an elevated line (ANY elevated line) is neither the cheapest nor the one of the least impact.  The cheapest is at-grade and the one of the least impact is underground.  The elevated line is exactly in between.

> The classic demonstration of the low noise impact is the Walt Disney World
> monorail operating through the lobby and dining area of the Contemporary
> Resort (photo).

A classic demonstration of the low noise impact is ANY subway line, which provides ZERO noise on the surface.  Without any accompanying pictures, because the visual impact is also ZERO, and thus there is absolutely nothing to picture.

The main point must be already clear: the elevated alignment is the most invasive of all, for whatever mode running on it.  At the same time, it is not the cheapest.  And thus there is rarely a need to build extensive elevated lines with 90% of line being elevated.  This is demonstrated by the simple fact that most of the newly built rapid transit systems are NOT elevated and do NOT have a substantial elevated portion.  Just take all the mileage built in the U.S. for the last ten years and estimate how large portion of it was built elevated. Independently of the mode, you'll see that less than 10% of everything built is actually elevated.  First thing first, and before providing pictures of the elevated structures, one must ask how common the elevated structures are and how needed the elevated structures are.  And it turns out that they are neither very common nor very needed.  For all the same reasons: high impact and not the lowest cost.  INDEPENDENTLY of the mode.

> This brought home the point that elevated conventional rail is often
> considered incompatible with residential and business areas.

Practically speaking, ANY elevated structure is often considered incompatible with residential and business areas, INDEPENDENTLY of the mode. That's why it is not commonly built.  There is no conspiracy here: people just don't want trains above their roofs (even if some monorail fans do). Recall that all the elevated lines in New York and Boston were ultimately replaced by subways, and the Chicago Loop is pretty much the only historical exception of an elevated structure in a downtown.

> If you want to see lists of advantages, see

Oh, please, don't make me laugh! This pathetic list of childish comparisons
cannot be taken seriously. These people do not seem to understand the difference between "mode" (heavy rail, light rail, monorail) and "alignment" (underground, elevated, at grade), and often they compare advantages and disadvantages of the alignments, failing to realize that some modes (like light rail) can be used on the entire variety of the alignments, while others are stuck to only one (monorails on the elevated structure). Some of their points really look like political propaganda, like "ugly trolley wires" (are the much bigger concrete beams less ugly?), which was used in the 1950s to dismantle many streetcar systems in the U.S. This is anything but a professional web-site. They should have hired at least some technical consultant who could tell them that comparing "street running" and "elevated structure" is NOT comparing "light rail" and "monorail". This is just a bunch of monorail fanatics who will make up anything you want just to say how good the monorail is. They simply twist the fact and the logic to fit their agenda.

> A less propagandistic (although still rather confused) listing of monorail pros and cons:

This is indeed a better piece. However, this one also fails to mention monorail's main disadvantage: the need for an elevated structure for an entire line. To my mind this is a very important limitation and the main reason monorails are not so widespread as their advocates want them to be.

People keep discussing the transit modes and comparing them, while forgetting that these modes operate in real cities, and the need for these lines must be traced back to the needs of the particular cities. Only very few cities really need entirely elevated lines for tens of kilometers, and so only few cities should really consider monorail. Many people who discuss monorails do not understand this. They just compare structures, beams, wires, and other technical aspects, while completely ignoring the fact this is a form of URBAN TRANSPORT, and it must be compared as urban transport (i.e. as a public transit SYSTEM) as well. And this is exactly where monorail looses big time.

Last update: October 15, 2006.