Bringing an updated rail transportation system to the Northeast corridor, one of the most densely developed and populated regions in the world, will be enormously expensive and complicated no matter what option is pursued. Yet it is also necessary. The United States has fallen far behind Europe and the developed areas of Asia when it comes to providing mass transportation options.

In the Northeast, our highways have grown overcrowded. While some highway improvements are necessary, including widening Interstate 95 as it travels through this region, the response to that congestion will also mean getting more people off the road and on to rail.

Moving people by rail is far more energy efficient than car travel, saving resources and reducing greenhouse emissions. It can also be more productive, with those traveling on business able to communicate and get work done while in transit.

By more efficiently tying cities together, a modern rail system can help drive economic development and expand commuter options.

Since 2012, the Federal Railroad Administration has been analyzing ways to modernize the Northeast corridor that serves the megalopolis running from Boston to Washington, D.C. The FRA expects to issue its recommendation from among three alternatives, or some combination of those choices, sometimes this fall.

Causing the most consternation locally is the least expensive alternative. It also makes the least sense.

For an estimated $64 billion investment (yes, that’s the lowest cost choice) the project would bring only modest changes. To supplement the existing shoreline tracks, an added spur a few miles inland would run from Kenyon, R.I., and reconnect with the existing line in Old Saybrook. This bypass would become the main line.

The same alternative also adds lines circulating around Baltimore and New York City.

Locally, that would move rail traffic away from New London, not a good prospect for its future development. The $10 billion to $15 billion bypass is also shown going through such local attractions as the Olde Mistick Village, the Mystic Aquarium property and the Florence Griswold Museum in Old Lyme, to name a few.

In other words, small improvement, big investment and major disruptions.

More compelling is a second plan that would add a new line running from Providence, R.I., across Northeast Connecticut, connecting with the University of Connecticut campus in Storrs and continuing to Hartford. Another new spur would carry riders from Hartford to New Haven. Existing shoreline tracks would carry local commuters.

These added, straight-line spurs would allow higher speed travel, provide more connections, and attract more riders. With connections to the existing line, it would increase riders to New London and other shoreline stops, rather than decrease them, as would the bypass.

More ambitious still, and backed by Amtrak President and CEO Joseph Boardman, is the third alternative that envisions multiple new lines connecting cities throughout southern New England, including Worcester, Mass., and Waterbury and Danbury in Connecticut. It also envisions a tunnel under Long Island Sound, taking riders to the center of Long Island, then west to New York City.

Plan 3 is exciting, the kind of big project the nation once entertained. But it is also incredibly expensive, an estimated $308 billion, and that’s probably conservative. It may well be too ambitious. The cost of Plan 2, or some hybrid alternative, would lie somewhere between the lowest and highest cost options.

To put these costs in some perspective, consider other massive public investments.

The national interstate highway system, signed into law by Republican President Dwight Eisenhower in 1956, took 35 years to build at an estimated cost of $511 billion in today’s dollars.

More recently, the Big Dig, taking Interstate 93 under Boston, cost nearly $20 billion. The Apollo program that landed men on the moon cost about $150 billion in adjusted dollars. The Pentagon estimates it will cost $97 billion to build 12 modern ballistic missile firing submarines to replace the Ohio-class fleet.

In addition to costs, the modern regulatory approval process, the process of land acquisition, and increased environmental sensitivity all present challenges greater than Eisenhower’s highway program confronted.

But if the nation is to undertake such a massive project as improving the Northeast rail corridor — and it should — going small is not worth the investment or the aggravation.