In addition to subways, elevated and light rail, Shanghai also has a maglev. 
The Miami Metrorail system is almost entirely elevated, with a few short sections at ground level. There are no underground sections.
For some reason tunnels in Miami doesn’t seem like such a good idea.
As noted above, the San Francisco Bay Area has BART (Bay Area Rapid Transit), portions of which are elevated, at ground level, and underground and even under water.
I attended a lecture, circa 1971, at BART headquarters in Oakland, given by BART officials and/or engineers, at which that was discussed. COST of building such systems was a MAJOR factor, but heavily affected also by practicalities.
Building track at ground level is by far the least expensive. This works best in outlying areas, or even in urban areas, but can cause problems with vehicle traffic because of all the grade crossings. Building at ground level in an already-built-up area also has practical difficulties in acquiring the necessary land and rights-of-way, and tearing down existing buildings and such.
Building elevated track is somewhat more expensive. In dense urban areas, it is still necessary to acquire the airspace needed for it. This might be a bit easier than getting ground-level real estate.
Building underground is VASTLY BY FAR the most expensive, and thus to be avoided if the other options are at all possible. This is most likely to happen in dense urban areas, where the system could be build beneath the streets. This was the choice in Berkeley and San Francisco and in portions of some of the surrounding areas. We were told that the city of Berkeley, for example, insisted on BART being built underground there. I’m going to guess that this was attended with much political wrangling about who would pay for some or all of that.
Thus, BART runs underground through portions of Oakland (particularly, downtown area), then is elevated as it heads north toward Berkeley, then goes underground again through Berkeley, then is elevated again as it heads into El Cerrito and Richmond, the next cities to the north. San Francisco is underground. Most of the rest of the system is elevated.
Come to think of it, I’m not sure if any of it is at ground level. There might be some ground level track from Oakland south to Fremont, in some of the less densely developed areas (at the time it was built, late 1960’s/early 1970’s). There, major crossings with automobile roads would be handled by having cars drive through an underpass or overpass. Now that I think of it (having been mostly away from the area for about 40 years) I don’t really recall if there is any ground-level track.
(Missed edit window, above.)
ETA: The eastern sections of the system (toward Walnut Creek and Richmond, and the newer segments towards Pleasanton) must go through a range of mountains to get there. For these sections, they had to dig tunnels through the hills. On the east side of those hills, portions of the track run down the middle of the freeways, which were apparently built in the first place, way back when, with enough space to add that.
It appears to me that major infrastructure systems like these are planned YEARS AND YEARS in advance, much more in advance that we might realize. Those freeways were built many years earlier, and yet when BART came along, there was room in the middle of the freeways for track there. I suspect they planned that all along, as far back as the 1950’s probably, when those freeway systems were being built.
You can see that in other areas too. The highway from Los Banos east to Route 99 runs through open corn fields mostly. Yet the eastbound and westbound sides are separated by an unpaved median that is at least as wide as the total paved width. This road has been there like, forever. Why would they build it like that? Obviously, to provide space for future expansion (e.g., extra lanes to be built later). Los Banos is a burgeoning community, becoming a longer-distance commuter bedroom community for Bay Area overflow. (They would have to be desperate to commute that far!) I think the transportation planners have it figured out, many decades in advance, where the growth is likely to be, and (again, decades in advance) build the roads (or at least acquire rights-of-ways) with plenty of expansion room accordingly.
But now, there is all this talk about building high-speed rail from Los Angeles to San Francisco. And, among the various routes often discussed, that same route (or something in that vicinity) is often mentioned. It wouldn’t surprise me if part of that rail line ran down the middle of the highway between Los Banos and Chowchilla, where it meets Route 99.
You can see similar things in some newer roads. In Fresno, there is a relatively new stretch of freeway running northeast out of town into the hills. There, too, one sees a very wide median, about as wide as the paved area, in the middle of a freeway that runs out into the boonies. Why waste all that real estate? Again, I think the planners see where the growth is going to be, 50-some years in the future, and they are planning for it now. That space could be used for more lanes, or maybe even for a future grade-level rail system.
Seattle might count, sort of. The monorail runs elevated from Seattle Center to downtown, which is the whole route. It’s still more of a curiosity, a leftover from the World’s Fair, than a practical transportation system. And there is a tunnel through downtown. Last I was there, it was used by electric buses, but there were rails installed with plans to expand the system and convert it to light rail.
Seattle dopers, is that still the plan, or has it happened already?
The Glasgow Subway is totally underground. It’s less than seven miles long.
Already happened - Light rail is in the bus tunnel (I still call it that, out of habit), and has some street running, underground and elevated sections south towards the airport. It will be expanding both north and east, eventually. The buses (most of which can switch from diesel to electric depending on where they are on their routes) still use the tunnel as well as street running.
Same in Paris. Part of the “subway” is in fact elevated lines.
That’s not necessarily the case. Several parts of the L.A. Metro, including the Orange Line busway and the Gold Line, travel down decommissioned sections of old railroads which occasionally were routed down the center of freeways. So it only looks pre-planned. The Glenn Anderson Freeway was indeed designed with the Green Line in mind, but that was built in 1993.
Throw down another one.
Washington, DC’s Metro system is - depending on where one is - below ground, above ground and at ground level.
The part of Philadelphia’s Market-Frankfort line through center city is underground and the other sections are elevated. The Broad Street line is entirely underground except for a short section around the Fern Rock station at the northern end.
This. NY, Chicago, Philadelphia, Boston, Paris among others I have used. In Brooklyn, the is at least one exchange (4th Ave. and 9th St.) where you can exchange between the F, which has just become elevated and the underground R. Of the two main lines in Philly, one is elevated for most of its route but underground through center city (and, since around 1960, a bit into West Philly). The other one is subway all the way. There are also streetcar lines in West Philly that are street running until they get to near center city when they go underground and join the subway (on side tracks, not the main line). Boston and San Francisco also has subway/surface streetcars.
The Montreal metro system is all underground and sheltered against the outside. That’s good in the winter, not so much in the summer and makes extensions expensive.
You never saw the Market-Frankfurt subway/elevated? I guess some of the old Pennsy lines were running near ground level but on their own rights of way and with trestles over intersecting streets. They still are. That includes the main line of the railroad, now operated by Amtrak. The same is true of the old Reading lines. Both those and the local rail on Pennsy track are now operated by SEPTA. The old P&W line also runs elevated for its entire route AFAIK. The old Red Arrow suburban lines were mostly street level but on their own rights of way. Name a light or heavy rail line in Philly and I’ve probably taken it.
We have a few, such as the Port of Miami Tunnel (coming soon). They are rare, and expensive to build.
Pointless fact. 55% of the London Underground is actually above ground.
There are other NYC stations where an elevated line intersects with an underground one. At 161st Street-Yankee Stadium in the Bronx, the 4 line (IRT) is elevated and the B/D station (IND) is underground.
The NYC system originally consisted of three separate systems, the IRT, BMT, and IND, which accounts for some of these anomalies.
Those aren’t the only possible exceptions. Cleveland’s rail system is entirely ground-level, with the exception of a single stop downtown that’s underground (well, under foundations). The Red Line mostly runs alongside railroad lines in trenches, with car traffic crossing over on bridges, while the Blue and Green lines mostly follow medians, and are subject to traffic signals at intersections.
Only on the route map posted in the cars. I guess I just never had occasion to travel anywhere on that route. Most of my experience with the public transit was going from Villanova to downtown and back (there was a Septa route and a light rail, but I can’t remember what either of them was called).
Tokyo has plenty of both. There is a fairly distinct pattern, as already noted. When a new rail line is built through an already developed urban area, it’s almost always a subway. Elevated rail lines are usually built in suburban areas, or to replace a surface rail line that already existed (to ease road congestion).
There are many elevated rail lines still left in the middle of Tokyo, mostly run by JR (Yamanote line, etc). Those were built when those areas were suburbs (Shibuya and Shinjuku used to be suburbs, which is hard to believe today). Most other commuter rail is underground, and some of them connect to elevated tracks in the suburbs.
Washington, DC has the same thing. Most of the stations within the city limits are underground, but a few aren’t. Stations outside the city limits in VA and MD are largely at-grade or elevated, but a few are underground.