Staten Island has no rail connection to the rest of New York City, but that’s not for lack of ideas. The oldest was a proposal back in the 1920s to build a tunnel, variously planned for either passenger traffic or passenger and freight, under the Narrows, a strait between Brooklyn and Staten Island. The rail line would have branched off what is now the Fourth Avenue line in Brooklyn, carrying D, N and R trains. The plan at one point shifted toward a bridge connection (the “Liberty Bridge,” it was then called), but when Robert Moses erected the Verrazano-Narrows Bridge in the much more auto-oriented post-war years, no provision was made for trains.

There have been occasional calls for reviving an R train extension, most notably by Republican mayoral candidate Joe Lhota. The R, however, is a painfully slow local service and Lhota is a longshot candidate, so these likely won’t lead anywhere.

Another more recent idea, proposed by transit blogger Alon Levy, would involve a much more useful, albeit expensive, extension of Metro-North’s commuter rail line down from Grand Central Terminal into Lower Manhattan and then onto the Staten Island Railway. This latter service runs the length of the island but currently only takes you to the ferry terminal at St. George, on Staten’s northernmost point, from which you have to take a half-hourly, 30-minute ferry across to the Financial District.

But perhaps the most promising idea isn’t a connection to Brooklyn or Manhattan, but to New Jersey.

Unlike the Verrazano-Narrows, the Bayonne Bridge connecting Bayonne, N.J. with Staten Island opened in 1931, before cars had captivated regional transportation planners. As such, pains were taken to build it so that it would allow a heavy rail connection in the future.

That rail connection was never built. But construction of the Hudson-Bergen Light Rail line in New Jersey, and its extension to Bayonne in 2011, means there is now a viable passenger train on the Jersey side of the bridge to connect with, should Staten Island build a line on its own side.

To that end, researchers at the City University of New York and — where else? — the University of Canberra in Australia have outlined a proposed route across Staten Island, building on the success of a recent bus line across the bridge. It would require regional cooperation that’s been lacking as of late, not to mention hundreds of millions of dollars, at least, in funding. Still, it’s the most likely option to come to fruition.

While Brooklyn or Manhattan might seem like a more natural link, Staten Island has become quite integrated into New Jersey in recent years, as there are many more transportation links to the west — in addition to the Bayonne Bridge, there’s the Goethals and the Outerbridge Crossing — than to the east, which just has the Verrazano-Narrows. A connection to New Jersey would offer many Staten Islanders a one-seat ride to the burgeoning secondary business district along the “Gold Coast,” which has sprouted a glassy forest of office towers housing back office operations for firms that seek cheaper space than what they could find in Manhattan.

The researchers use the S89 bus service on Staten Island to prove that the demand exists. Established in 2007, the bus route has built up a ridership that mostly uses it to transfer to the Hudson-Bergen Light Rail line, which travels up the Gold Coast to Jersey City and Hoboken (where some people presumably transfer to the PATH subway into Manhattan). While the service only attracted 927 riders on average each weekday, this number is pretty impressive when you realize how limited the service is: Only 18 runs in each direction on weekdays, and no service at all during the middle of the day, at night and on weekends.

With beefed up hours and a seamless connection to New Jersey that doesn’t require a transfer — not to mention more comfortable and faster light rail train sets — this number would surely grow. The researchers don’t hold up the current S89 as necessarily the best route for a new light rail line, but use it to point out that there is demand for such a service, even with paltry hours of operation.

Staten Island is the fastest-growing borough in New York City, and if it’s ever to densify and become an integral part of the five boroughs, it will require a direct connection to Manhattan. But until then, an extension of the light rail line across the Bayonne Bridge seems like the cheapest way to offer a rail connection off the island.