In the future…
Subterranean travel expands across the world, allowing for people to be conveyed from one location to another along relatively straight paths. These subways also traverse the center lane of many of the world’s major highways, and eventually come to be the major mode of transportation globally...

With the massive expansion and interconnection of the subways, subway platforms are social meccas for people to gather on daily. The intercontinental connections that can be made on these Platforms are exploited in every possible way. Whole communities are built near the Platforms, and are populated almost exclusively by families of conductors. Men, women, and older teens that have graduated from a magnetic conduction engineering program, offered in the first two years of high school, can operate a train...

Social gatherings on the Platforms function more like market places than waiting stations for trains. Most people on the Platforms are not even waiting for the train, but rather are waiting for passengers for various reasons. Hence the need for a monitoring force that polices the actions of the Platforms. They are a response force that operates with non-lethal force so as not to present such a threat that people will not feel such a sudden panic from their presence, causing them to possibly jump in front of a moving train...

1. If they are subterranean, why bother following highways? The only reason I could see for this would be above-ground sections, which more or less defeats the "social community" aspect. It would also tend to work against the "straight line" layout.

2. A much simpler enforcement mechanism would be a gate. Just don't allow non-riders on the platform. This is something that your story must deal with.

3. I don't buy the idea that the mere threat of lethal force might cause someone to panic and "leap in front of a train." Most people wouldn't run into traffic just because there are armed policemen on the sidewalk. I rode the Washington, D.C. Metro for years, and there are armed security officers around. People just get used to them like any regular policeman.

4. There's a neat seed in the idea of the somewhat insulated communities of Conductors and their families. Lots of possibilities there. That's where I'd be looking for a story.

5. You might want to consider having your "social meccas" aboveground, with limited access to the belowground embarkation points. Also keep in mind Mike's point about explaining how and why these "meccas" formed.

6. The basic purpose of subways is to get people from work to home and vice-versa. If there's too much community around the Platforms, people won't need the subway.

7. The issue of a trans-continental subway or railway shouldn't be taken lightly. I watched a show (on Discovery or something) on the engineering issues involved in such an endeavor. One major one is speed: Even the high-speed "bullet trains" operate around only 135 mph, and maglevs max out around 300 (the speed record is somewhere around 350, I think). Consider that a 747 can fly at 570 mph (airliners can climb to altitudes where air is less dense, trains can't). Even assuming a 100 mph difference, when you figure that the narrowest part of the Atlantic is over 1700 miles wide, you're looking at about a 45 minute difference in travel time. You'll have to somehow make the trains at least as fast and probably faster than air travel to make it economically viable.

It can be done; you can just brazen it out, Michael Marshall Smith style. But while his first book (Only Forward) got away with it because of its originality and sheer verve, it's my opinion that subsequently, the second (Spares) just came over as unbelievable.

As I recall, the subway stations of New York generally filled with businesses, retail stores of some kind. I remember an oldies record store off the Times Square stop (I think---I never visited but I heard of it).

I don't know that people would locate their residences inside a Platform...they'd locate near them, of course, because communities spring up around ports or railheads or airports.

Where would these Platforms be built? Likely under existing cities...probably there'd be points of connection requiring passengers to switch trains...likely new cities around them.

If you set your story on a Platform at a connection point under the ocean, it would introduce a whole new layer of technical complications in your story.

I have a friend who is a retired engineer from a local railroad. Ever wonder why you never see any weeds growing up around railroad tracks? There are issues of the railroad spraying heavy amounts of herbicides, close to waterways (My community is on a large river). The railroad is loathe to admit this, particularly since a lot of the fish and wildlife along the railways are protected. (Lots of salmon and bald eagles out here.)

My friend has commented on cover-ups relating to blatant disregard of safety laws. He used to be on the safety review team and knows of a specific incident where someone was killed at a crossing he cited in one of his reports, due to the very safety violations he cautioned the railroad about. This case is making its way to trial.

Anyway, that adds more possibility to your story.

I may not have understood what you were saying about the cops. Anyway our cops are supposed to use nonlethal force, almost all the time; for UK cops, it's nearly universal. But even in places where the "cops" carry machine guns, people won't flee from them into certain death.

I think you could get away with the platforms becoming social hubs if people often need to switch trains--sort of like the places where highways cross, or even more relevantly, subway stations that connect different lines. The trains could cross underground, so that's where businesses see commuters (probably wealthy ones if they need to travel so far) as fair game. You could even throw in some added incentive relating to unclear tax codes due to issues of zoning or some nonsense.

As for the police, it sounds like it's important to your plot that the police are trained in non-lethal combat. Why not just throw in there that the modern weapon of choice for police--some sort of energy weapon--interferes locally with the fancynamehere railway tech that allows the trains to achieve their amazingly fast speeds? Two birds, one stone.

As far as the social mecca, I agree that would take some fleshing out. It is one thing to look at a train platform at 7 a.m. and see high school kids meeting each other there, then spending the next half hour socializing. I'm trying to expand that idea.