Advantages of Underground Rail

Well, if I'm going to talk about the advantages of elevated rail, it feels only fair to discuss some other advantages: like the advantages of the other main grade-separation option, underground rail.

Because if there weren't any, well, we'd all build the cheaper, elevated option, wouldn't we?

Note that when I say "we," of course, I don't mean the Quad Cities. Lord no! It would be nice, but let's get some basic bus frequency and maybe a rail link to Chicago first.

But "we" in the larger sense do keep building tunneled, or cut-and-cover, rail: so why? What is it bringing to (or rather, under) the table?

1. Land Use

Probably the most obvious advantage of underground rail, besides grade separation itself, is that it has limited demands on the surface: while it requires just as much space as anything else when you consider the space underground, we as a society tend to value the surface much more than the depths: we live there, after all.

That means that a form of transportation whose visible surface-level footprint is minimal has big advantages.

This space doesn't count: the platform, the tracks, the rest of it is all under the everyday life of the city.

Even a big suburban station like this one on the Toronto-York border is still just a single building at the street level.

When your footprint is small enough you need an actual sign for anyone to know it's there, that's small.

2. Unexpected Connections and Paths

The knock-on effect of putting all the actual train stuff down underneath everything is that you're not as constrained by the surface-level patterns in terms of where you put the tracks or stations. True, it's very expensive to tunnel under a river or through a mountain, and going through dense areas has its own problems (good luck avoiding all the other hidden underground systems on which modern cities depend, like sewers, electrical, etc.) but whereas elevated rail tends to mirror or mimic street grid patterns because otherwise you have to knock down the buildings in the way, underground rail...doesn't have to do that.

This could go anywhere! It's like a portal to Narnia, if Narnia had a metro sign instead of a lamppost.

That's how you can build something like Crossrail (now the Elizabeth Line) and connect a bunch of destinations that weren't previously connected: you have (assuming political will and budget) substantial freedom in how you zigzag beneath everything else.

3. Whether the Weather...

And of course, underground rail is out of the way of the biggest objection to elevated rail: the weather. Now, the London Underground may be constantly overheating itself, but by and large you have more control over the temperature and the (hopefully non-existent) precipitation underground than above.

Platform screen doors make this even more pronounced, as you can do more to the platforms as well as the actual cars themselves.

Pictured: a space that will only be rained on in an absolute disaster. 

Now, do these advantages counteract the advantages of elevated rail we looked at before? Of course not. Otherwise we'd build only one kind of rail. But they are significant, and they offset the generally greater cost of underground rail substantially. That's why both are viable options--and why, if we can afford it, a lot of cities opt for going underground.