The commuter rail line that was to snake from North Raleigh through Cary to Durham, perhaps some day all the way to Chapel Hill, might have soaked up mega-millions in planning, engineering and real estate costs, but whether anything like it will ever actually be built remains a mystery.

Intercity bus service has been ramped up, but as highways become even more clogged, it's not hard to see a point of diminishing returns. If taking the bus is just going to mean sitting in traffic on I-40, the temptation will be strong to do that sitting in one's personal chariot instead.

After Uncle Sam told the Triangle Transit Authority that its commuter rail project wouldn't qualify for federal money, the region had to face the fact that whatever it wanted in the way of a transit system would have to be paid for essentially out of its own pocket. Charlotte, with its new light rail line, was the operative example.

A bevy of civic leaders was assigned to scope out a Plan B. At first, the consensus seemed to be leaning toward an updated, improved version of the defunct TTA scheme. But then cooler heads -- or perhaps folks with colder feet -- had their say.

Regional rail still looks to be a goal, but the sense seems to be that any declaration in support of a bona fide commuter rail system linking the whole area from the outset would be viewed as too grandiose. All the thorny cost-vs.-ridership issues that sank the TTA plan would be back on the table. The alternative? Roll out lots more buses. Meanwhile, build a little bit of rail here and a little bit there, and someday, maybe, hook the pieces together.

Here are a couple of numbers that you'd think would help light a fire under this process: 50 and 50.

Their significance? According to the U.S. Census Bureau, Wake County's population has been projected to increase by 50 percent between 2005 and 2020 -- at which time it's likely to be home to 1.13 million people. Johnston County, Wake's next-door neighbor to the southeast, likewise is due for a 50 percent population rise to 219,000, the census folks say. The counties are on track to be the state's third- and fourth-fastest growing.

What these numbers -- part of a presentation for editorial page staffers last weekend at UNC-Chapel Hill -- suggest is that if you think traffic on the main Wake-Johnston connectors is bad now, it's on its way to becoming truly horrible.

You've seen the rush-hour jams on I-40 and U.S. 70, as people from southeastern Wake and northwestern Johnston surge toward downtown Raleigh and Research Triangle Park in the morning and back again at night. At the editorial roundtable, we also learned that, according to a Census survey, 40.3 percent of Johnston's work force was commuting into Wake. That amounted to 23,628 people -- and no doubt almost as many cars.

What if those drivers had an option? What if a rail line ran more or less parallel to the main highways, through Johnston's boom town of Clayton, into downtown Raleigh and thence to the Park?

The good news, of course, is that there's no "what if" about it. The N.C. Railroad's tracks do just that -- a commuter rail opportunity waiting to be seized if there ever were one.

And even better, the state-owned railroad company is in the middle of figuring out how it could best grab hold.

The N.C.R.R., whose tracks run from Morehead City to Charlotte, has a study under way of what it would take to offer commuter rail service within the stretch between Goldsboro and Greensboro.

President Scott Saylor told me the model he has in mind is the Virginia Railway Express, which funnels commuters from the Northern Virginia suburbs into Washington. The link southeast of Raleigh into Johnston and possibly beyond toward Goldsboro has particular promise, Saylor said, because competition from freight trains is less intense. He envisions four passenger trains in the morning, four in the evening and one during midday.

That sort of service would not be on the same level as the frequent trains envisioned by the TTA. But there seems to be a logic to it that was elusive in the earlier plan, which would have had North Raleighites who work in RTP going around their elbows to get to their thumbs.

As the Triangle -- with the city of Cary, it's more of a Quadrilateral -- continues to grow, the need for a dependable transit system providing an alternative to cars will become even more glaring. But given actual development and commuting patterns in 2008, as opposed to when the TTA plan was conceived a couple of decades ago, the market for transit options clearly ranges into Johnston County.

Do we need a Wake-Johnston planning effort to make sure this puzzle comes together? Whatever it takes, I'd say, to give those Johns-tonians a good ride to work while keeping cars in the driveway.