So much for the adage, "Build it and they will come."

After several decades and $1.2 billion, the Pennsylvania Turnpike administration has finished about half of the Mon-Fayette Expressway, conceived as a modern route to Pittsburgh and a catalyst for economic revitalization for old towns in the once-booming Monongahela River corridor.

Not only is population dropping or static along portions of the limited-access toll road through Fayette and Washington counties, but expressway traffic is down as much as 18 percent on the first section that opened in 1990 -- six miles of tolled highway south of Interstate 70 and a convenient way to California University of Pennsylvania.

Some officials see the lower number of users after years of slow growth as a glitch, partly because of high energy prices, partly because of a general economic slowdown and partly because the 24-mile northern section has not been built in Allegheny County to where most people want to go: Downtown, Oakland and Monroeville.

"As we make the connections, you'll see more traffic and more development," said Joe Kirk, an aggressive advocate of the toll road since he was hired 20 years ago as executive director of the Mon Valley Progress Council. "Unless that happens, [the expressway] is not going to achieve its total goal."

After observing traffic recently at various locations in Fayette and Washington counties and in Jefferson Hills, the Post-Gazette found the Mon-Fayette Expressway to be a mostly lonesome highway.

For example, between 7 and 7:30 p.m. on Sept. 2, a Tuesday, only 34 vehicles passed in both directions on the 6.4-mile section south of Uniontown. Cars were so few and far between that kids on all-terrain vehicles crossed the highway, albeit illegally, to reach paths they've created in adjacent woods and fields.

A different place and different time saw better results. A total of 176 vehicles passed the PG's checkpoint in both directions between 5:15 and 5:30 p.m. at the mainline toll barrier near Route 51 in Large, on Aug. 29, a Friday, at the start of the Labor Day weekend.

But over that same 17-mile section, south to Interstate 70 in Fallowfield, only 18 cars were counted in both directions between 12:30 and 12:45 a.m. Aug. 24.

Some motorists enjoy being able to drive up to 65 mph with nary anyone in front or behind them.

Larry Drill, of Marianna, has driven the expressway between I-70 and Route 51 since it opened in April 2002.

"I am one of only 10 cars that use the expressway at 7 a.m.," he said. "When I traveled inbound on Sunday afternoon of the Labor Day weekend, there were only three cars."

Chris Seymour, of the South Side Slopes, used to take the original stretch from I-70 to Route 40 in Brownsville to visit his grandmothers in Uniontown in the 1990s.

"While it was a pretty quick way to get there, I rarely saw anyone on the road," he said. "I no longer have family there, but when I traveled the road once or twice recently, it was still deserted."

The Pennsylvania Turnpike Commission, which the state Legislature directed to build the Mon-Fayette Expressway in the mid-1980s, is currently spending $850 million to close a 17-mile gap between Uniontown and Brownsville. When finished in 2011, 57 continuous miles will be open.

Also that year, West Virginia should finish closing a 3-mile gap south of the Pennsylvania border to I-68 near Cheat Lake, making the expressway attractive for travel to Morgantown.

The future, however, is uncertain for the 24-mile, Y-shaped northern end to Pittsburgh and Monroeville, the final section, whose estimated cost is rapidly approaching the $4 billion mark because it lies in an urban area and crosses challenging terrain.

Because of that high cost, turnpike officials will hold a meeting Wednesday in Harrisburg, hoping to interest potential investors in a public-private partnership. In exchange for finishing all or part of the Mon-Fayette Expressway and related Southern Beltway, the turnpike is offering to throw in the rest of both toll roads for free as part of a deal.

If that's a way to get the roads built, so be it, said state Sen. Barry Stout, D-Bentleyville, Democrat chairman of the Senate Transportation Committee and the project's biggest legislative booster.

"I'm as totally committed today as I was in 1970, when the Mon-Fayette Expressway wasn't a cubic yard of concrete," he said. "Soon we'll have 57 miles. This is a road we're building for the future, for our grandchildren, so they won't have to leave southwestern Pennsylvania to work and live."

When the first section of the expressway was dedicated Oct. 12, 1990, the 6-mile section south of I-70 near California University of Pennsylvania, Sen. Stout yelled, "Let the quarters flow," as the late Gov. Robert P. Casey drove through a toll booth.

The toll there has since been raised by a quarter, to 75 cents, and will likely go to $1 next year, which doesn't bode well for a stretch where average daily traffic dropped to 8,723 trips a day in May compared to 10,650 in May 2007.

The I-70 to Route 51 section was averaging 10,624 trips per day in May, about a 16 percent drop over the same period the previous year.

The number of daily trips on the "Mason Dixon Link" south of Uniontown remained around 2,500.

"We believe the drop-offs in Washington County to be almost entirely due to higher fuel costs," turnpike spokesman Joe Agnello said. "The numbers seem to be coming back up again."

Turnpike records for the two most recent budget years show small gains for such a large investment of public funds and so many miles of limited-access, high-speed highway.

Total traffic volumes increased by 248,076, to 8.8 million for all parts of the Mon-Fayette Expressway for the 2007-08 fiscal year compared to the previous year, while total revenues increased by $163,260, to $6,657,716 -- both less than 3 percent.

Mr. Agnello said, though, that revenues were more than sufficient to cover operating expenses of $4.1 million for everything from the light bill to state police patrols.

Mr. Kirk said although traffic may lag behind expectations, the public investment in the expressway has meant more than an open road for users.

He provided a 2002 study showing the project had attracted 14 companies that made $31.7 million in private investments and provided 694 jobs in four industrial parks.

"Since then, there have been others," he said, including a 300-unit residential development where 75 units have already been built near Finleyville, and expansion at Mon Valley Hospital.

"When the highway is finished, it will live up to promises," Mr. Stout said. "I'm not disheartened."