As well as having the world’s largest metro system by number of stations, New York City also has a pretty sizeable commuter rail network.

In fact, it has several. There’s the MTA Metro-North Railroad, run by the city’s Metropolitan Transit Authority, which serves the northern suburbs in New York state and Connecticut. There’s the Long Island Rail Road, and the Staten Island Railway: those are also run by the MTA, and respectively serve, well, you can probably guess. And then there’s the NJ Transit rail network, run by the authorities in the adjacent state of New Jersey, which serves that state and a few counties in its neighbours.

Between them, these four different systems carry passengers to and from the city from all points of the compass. But the system is fragmented: to get from Staten Island to Manhattan, you need to take a ferry. Some of the trains from New Jersey run into Penn station, in midtown Manhattan; but capacity constraints mean that many others terminate across the Hudson in Hoboken, requiring passengers to change to a PATH train, and then probably again onto a subway.

It’s a measure of the network’s complete lack of integration, in fact, that there is, best we can tell, no official map which shows all of it – even though some NJ Transit trains magically turn into MetroNorth ones at the state boundary. All seems a bit silly to me, but there we are.

None of this seems very likely to change any time soon, if ever – but in 2015, some city planning students at the University of Pennsylvania School of Design did at least propose a start.  Here, inevitably, is a map:

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The New York-New Jersey CrossRail project would involve a capital “R”, as well as a pair of new tunnels under the metropolis. These would run from Newark in New Jersey, through Penn Station and out to Jamaica in the suburbs of Queens. There’d also be branches connecting to Newark and JFK airports, and another heading north to link up with Metro North services.

All this would mean that the current service would change from this…

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…to this:

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The big benefit of such a scheme is that it would make it much easier to get across the Hudson. No new transit tunnels under the river which divides New York from New Jersey have been built since 1910, and those which do exist are at full capacity. The existing Hudson River tunnels, the CrossRail team wrote, “are the most significant choke point along the entire Northeast Corridor”.

The proposed new tunnel will remove this bottleneck. It’d also make it easier for residents of Queens to get to Manhattan, relieving chunks of the subway network, too. And as a bonus, it’d open up new real estate schemes along the route, generating at least some of the cash which would pay for it.

How realistic is this? It is fundamentally the work of some students (albeit pretty well qualified ones), rather than an official proposal. And building new rail capacity in New York has proven to be both difficult and incredibly expensive. The recently opened second Avenue Subway extension has been called the most expensive subway ever built: nearly $4.5bn for just two miles of line, which would be hilarious were it not for the fact that stuff like this makes it harder to persuade politicians to invest in this stuff.

But CrossRail isn’t a complete pipedream. The students’ proposal builds on two official ones: Amtrak’s proposed Gateway project, which would build a new tunnel under the Hudson and expand Penn station, and the MTA’s Penn Station Access project, which would take Metro North through Queens into Penn Station. What CrossRail does is to combine these, and to continue the route to the east, out towards Jamaica and Long Island.

There’s lots more nerdery in the report, about financing, phasing construction, service patterns and so on. But odds are you came here mainly for the maps, so let’s end on this one, which compares the proposed New York CrossRail with the nearly completed scheme which inspired it:

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You can read more about the proposal here.

Jonn Elledge is the editor of CityMetric. He is on Twitter, far too much, as @jonnelledge.

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