Lights illuminate Hoover Dam at dusk Thursday as concrete columns, upper left, begin to rise a quarter-mile south of the dam on the Nevada side from what will be the base of a bridge spanning the Colorado River. U.S. Highway 93 traffic that now drives atop the dam will be rerouted to the bridge when the 1,905-foot span opens in late 2008. The engineer overseeing the project said it is 45 percent complete. Photo by K.M. Cannon.

If you've been waiting for the piles of dirt, concrete and steel at the Hoover Dam bypass bridge work site to start looking like a bridge, you'll soon be satisfied.

Immense concrete arches that will support the bridge's middle section could start being put in place as soon as October, as bridge construction work a quarter-mile south of the dam in Black Canyon now nears the halfway point.

Engineers say the project is picking up its pace as work continues on both sides of the Colorado River, where the first of 500 concrete columns are now being set up to hold up each end of the future span.

"We really are pleased with where we're at. The job is gaining momentum," Dave Zanetell, a Federal Highway Administration engineer overseeing the bridge work, said Friday.

Zanetell estimated the $234 million project is 45 percent complete, and back on schedule after a challenging springtime.

"We had a tough spring, in terms of a lot of wind, really having to grind to get things into position," Zanetell said. "We lost a number of (work) days to wind."

Zanetell said the bridge should be ready for its scheduled opening in late 2008.

"We're going to have to do well, but we intend to do well," Zanetell said.

The 1,905-foot, four-lane bridge will carry U.S. Highway 93 traffic now crossing the two lanes atop the dam. The bridge, which will stand 890 feet over the river, will be the longest concrete arch in the United States.

At the work site, precast columns are now being driven into the ground. Overhead, 2,300-foot cables strung up between 300-foot towers work as a type of pulley crane, carrying workers and materials weighing up to 50 tons more than 1,100 feet above the river.

"That's essentially the same technology today that was used in a very similar way in the construction of the Hoover Dam," Zanetell said.

Approach roads and interchanges are already complete. Zanetell said U.S. 93 commuters should not encounter traffic disruptions like those this past spring, when dam traffic was restricted at times to allow for work.

Regarding any future road restrictions, "those are very, very minimal" in nature, Zanetell said.

As many as 40 workers at a time are working round-the-clock at the construction site, according to Zanetell.

A legal spat between Clark County and the project's sole concrete supplier, Casino Ready Mix Inc. of Las Vegas, has not disrupted work.

"We continue to keep our eye on it," Zanetell said. "The bottom line is, we've been able to continue without impact."

County officials want to shut down Casino Ready Mix's concrete batching plant after rejecting its land-use permit. Company officials believe that rejection wasn't legally justified.

Both sides have agreed to allow the plant to continue operating until a Clark County judge rules on the matter. A ruling is expected soon.

The bypass project's managers are providing occasional updates on the Internet, including bridge facts, status reports, a Web cam and a construction photo album.