State transportation officials will close a section of the H-1 Freeway near the Waimalu viaduct for several nights next month to complete a lane-widening project expected to boost capacity in the area by up to 1,400 commuters an hour.

The $55 million project on the mauka side of the freeway, between the Kaonohi Street overpass and the Pearl City offramp, is nearly finished but workers still need to join the new lane with the old freeway with a 5-foot-wide, 1,245-foot-long ribbon of concrete, said Rod Haraga, director of the Department of Transportation.

The freeway narrows from six to five lanes at Kaonohi Street causing a bottleneck. Another bottleneck starts where the H-1, H-3 and Moanalua freeways come together.

Where the lane is being widened, an average of 226,000 commuters a day use the entire freeway. The evening commute gets ugly, though, as 'Ewa-bound drivers near the off-ramp.

The improvement will be considerable, Haraga said.

"At Kaonohi Street they will come straight on in and what you will see is a speed-up in traffic," he said.

The wider lane, which should be ready by April, comes as city officials discuss mass transit options for O'ahu that could cost taxpayers $2.8 billion. Neither project alone solves the island's traffic congestion problems, Haraga said.

"I think in conjunction with mass transit, you have to do other things, whether it is a ferry system or widening a lane," he said. "You will always have congestion. It is just how much you are willing to tolerate."

Transportation officials have said before that a mass transit project most likely will not reduce congestion on O'ahu roadways. Even with development of a mass transit system, traffic congestion and delays on O'ahu are expected to increase dramatically in the next 25 years because of continuing growth, especially in the 'Ewa Plains.

The city is considering a mass transit system that likely will stretch almost 23 miles between Kapolei and the University of Hawai'i-Manoa.

Transportation officials shut down the same area once before when they began the project in July 2004, said department spokesman Scott Ishikawa. Exact detours will be announced before the closure, he said.

Widening the lane is a simple job and doesn't even involve a lot of concrete because the ribbon is only 9 inches deep, Haraga said, standing on the new lane as waves of passing vehicles rushed by. In order for the concrete surfaces to bond with each other, the area must be free of vibrations during the pour, he said, and each time cars sped by, the new lane shook beneath his shoes for emphasis.

"We don't want the rocks in the concrete to settle," Haraga said. "If you overvibrate it all the rocks go to the bottom and the concrete is useless."

Reach Mike Gordon at mgordon@honoluluadvertiser.com.