ST. LOUIS -- The Big Detour is nearly over for metro-area drivers.

Five miles of rebuilt Highway 40 between Interstate 170 and Kingshighway will reopen to motorists on Monday morning, Dec. 7 — more than three weeks ahead of schedule.

The announcement on Friday confirmed what state highway officials had been hinting for months: The state's largest highway project would be completed early and below projected costs.

"People didn't think big projects could be delivered on time or in budget," said Pete Rahn, director of the Missouri Department of Transportation.

The half-billion-dollar initiative focused on a 10-mile stretch of aging highway that was in critical need of upgrades. The highway was rebuilt along with 29 bridges and interchanges over the last two years.

But it was Missouri's decision to shut town the thoroughfare in two, one-year increments that generated the most public debate. More than 120,000 vehicles a day traveled Highway 40 (Interstate 64) prior to its closure, meaning tens of thousands of motorists would be diverted to city streets, different highways and, in some cases, public transportation.

But fears of major traffic gridlock never materialized after the first five-mile leg between Ballas Road and I-170 was closed in January 2008. Commuters altered their work hours. Extra lanes were painted on Interstates 44 and 70. Local agencies tinkered with traffic light sequencing on heavily used roads to keep cars moving. Many of those adjustments carried over to the second shutdown the following year.

"What we had was enough time to change some of our processes and ways of communicating with our patients that really did make this a nonevent," said June Fowler, spokeswoman for BJC Healthcare. "Patients were able to get here."

Among facilities operated by BJC are Barnes-Jewish Hospital and St. Louis Children's Hospital in the Central West End, the BJC Learning Institute in Brentwood and Missouri Baptist Medical Center at Highway 40 and Ballas Road.

Fowler said the interchange at Kingshighway and Highway 40 should work better than the old one, and that traffic flows on Kingshighway already have improved.

"The skeptics were shown it can be done," said St. Louis Mayor Francis Slay.

Still, there were disruptions.

Richmond Heights Mayor Jim Beck said the project took its toll on his community. The state purchased more than 60 houses in the path of the highway, and another 79 properties lost some of their land. Many businesses suffered during the highway closures, Beck noted.

"It has been two years of really harsh times on Richmond Heights," he said, adding that he is happy the highway will be completed ahead of schedule.

Indeed, the early reopening should be a boost to nearby merchants who have seen their sales slump during the closures. St. Louis County Executive Charlie A. Dooley termed it an "early Christmas present" for shoppers and retailers.

"That it will be open before the holiday season really gets into full swing is great for everybody," said Brentwood Mayor Pat Kelly.

And the reopening will be lucrative for Gateway Constructors, the contracting team rebuilding the highway.

By completing the project on time, Gateway will collect $5 million in incentives — $2 million for meeting last year's deadline for the western half of the job; $2 million for timely work on the eastern half; and $1 million "for ensuring regional mobility during the project."

Rahn noted that the project's completion also means Missouri will lose an unenviable distinction.

"We will no longer be the only state in the country with an interstate highway that terminates in a Target parking lot," he said, referring to the store at the Brentwood Promenade shopping center where Interstate 170 came to an end before the project began. That highway now connects to Highway 40 via new flyover ramps.

A party will be held on a portion of the newly completed interstate to celebrate the reopening on Dec. 6, a Sunday, culminating with a ribbon-cutting at 3 p.m. Then, the highway officially will open before 5 a.m. Dec. 7.

Transportation Department officials said some minor work will continue after the reopening, such as grading and landscaping. But the highway itself will be complete, said Ed Hassinger, MoDOT's district engineer in St. Louis.

"It's going to look like a finished product."