HOUSTON (AP) — The biggest public works project in Harris County history is stuck in the mud — and that's a good thing.

The Houston Chronicle reports crews are tying steel and drilling deep into the mud along the Houston Ship Channel — among the first steps of significant work to replace the bridge carrying the Sam Houston Tollway across the ship channel.

When finished in the middle of the next decade, the bridge project will give drivers twice as many lanes, four in each direction, along with shoulders and a more gradual climb than the steep grade that anyone driving behind a heavy truck knows can be slow-going.

"It's one of the county's great needs," Commissioner Jack Morman said during a recent, soggy tour of the site where crews are planning for the massive foundations.

Work started along the ship channel's shoreline in April, but has ramped up recently as crews assembled the massive cranes that commuters will see for the new few years.

At roughly $1 billion, paid for via toll revenues, it is also county government's most expensive single project in history. Morman said approving the expensive contract didn't give him any concern, however.

"It kind of put things in perspective, but no, I wasn't worried," he said, noting the explosive growth of the region and the need to make the tollway four lanes in each direction throughout Harris County.

About 60,000 vehicles cross the bridge daily. With a huge jump in truck traffic and commuters, officials expect that number to swell to 158,000 vehicles a day by 2035.

The project launches with a long list of superlatives and a slight change from early descriptions. Plans call for replacing the Ship Channel Bridge with two one-way bridges of four lanes each. The twin spans will be side-by-side and connected at key points, such as at the two massive towers that hold all of the cables related to the cable-stay design.

The towers will be among the tallest structures in the region, slightly taller than downtown's Market Square Tower and slightly shorter than the Penzoil Place twin skyscrapers. The distance between the main towers, 1,320 feet, will make the bridges the sixth-longest main spans in the nation and second-longest in Texas, behind the new Harbor Bridge in Corpus Christi set to open in 2020.

Ship Channel Constructors, a joint venture of Traylor Bros. and Zachry Construction Corp., won the $962 million construction job. The cable-stay spans were designed by the Dallas office of Figg Bridge Group.

Per terms of the contract with Harris County Toll Road Authority, or HCTRA, the companies declined comment and referred questions to the toll road authority.

Officials settled early on cable-stay, which features two large towers securely anchored to hold up the roadway, which is fused together and tied in places to the cables. The towers bear all the weight.

The Harbor Bridge construction, which Harris County officials recently toured, is also cable-stayed. Figg was also the lead designer on that bridge, which like the Ship Channel replacement must cross a vast and active economic corridor.

"For something with a span this long, it really is cost-wise the most effective," said Steve Hague, project manager for the Ship Channel Bridge replacement with HNTB, which the county hired to oversee construction.

Like suspension bridges such as the Golden Gate Bridge in California, cable-stay bridges have a distinctive design and become major parts of the skyline around them.

For Harris County, the aesthetic was an add-on, and there are plans to light the towers. But the primary goal was to have four lanes and shoulders for safety.

"We definitely want function over form," Morman said on a recent visit to the construction area.

The two massive towers, forming what appears to be a double-X pattern, will dwarf the nearby plants and pipelines. East of Houston's business district, the only thing taller — and by less than 55 feet — will be the San Jacinto Monument.

In Houston, the bridges will be built separately, starting with the southbound span. That bridge will be completed and traffic moved onto it, so crews can then demolish the existing bridge and build the northbound span.

When both are finished in 2024 or 2025, the tollway will be four lanes in each direction with 10-foot shoulders on each side, giving drivers two more lanes and some much-needed breathing room on the sides.

"Thank you, Jesus," Beth Harper, 60, said when told about the shoulders. "It's terrifying, when there is a truck anywhere near you, to be on that bridge."

In many respects, the spans are a bigger and, officials say, better version of the Fred Hartman Bridge on Texas 146, another cable-stay bridge with two towering columns that carries traffic across the ship channel.

The new project goes through one of the most active shipping lanes in the country. It also crosses 106 pipelines, some carrying chemicals so dastardly that specifics were not shared with toll road officials by federal homeland security authorities.

Only two pipelines needed to be relocated because of the work.

Add to that the fact toll road officials cannot simply shut down the tollway, and the new bridges are shaping to be one of the most complex construction projects ever considered in the Houston area.

Yet construction is not expected to significantly slow down drivers.

"It is going to take us about a year to get out of the ground," said John Tyler, the toll road authority's deputy director and head of its engineering operations.

Despite the road and towers cutting an imposing figure along the ship channel, nearly half the concrete for the project will lie underground.

To secure the towers in the swampy mud along the ship channel, crews will use 97 concrete shafts poured into the ground, 48 for the southern foundation and 49 for the northern foundation. Just as someone would dig a hole for a fencepost and let the ground do the work of securing the post and keeping it steady, the towers must be solidly grounded.

That's the job of the shafts, some embedded as far as 240 feet into the earth, that will lie beneath a 20-foot-tall concrete pedestal. It is from those that the towers will be constructed out of hollow concrete.

"If it was solid, it'd weigh too much," Tyler said.

The project still has plenty of weight, notably in the roadway. The tollway approaching and across the bridge will be made of sections, allowing crews to put the pieces together. Think of it like a giant Lego set made of concrete, held together by wires.

The segments, nearly 82 feet wide and 16 feet tall, are nine feet, three inches wide. Building from the two towers, crews will work their way farther from the towers, placing on segment on one side of the tower and then moving to the other side.

"You will do one on one side and two on the other," Tyler said.

As they move away from the towers, there will be a total of 584 segments, with 128 of those connected to the wires and then locked to the others. There are eight segments until the next cable is placed.

The segments weigh 125 tons each and will be pre-cast at the construction site. Because the pieces must fit and match exactly, connecting pieces will be cast together.

The companies have leased vacant land adjacent to the job site where they will stack bridge sections until they are ready for use.

Once the southbound bridge is up and ready for traffic in about four years, crews will shift vehicles to the new bridge — divided with two lanes in each direction — and demolish the existing bridge, built in 1982.

"Really, in bridge age, it is a teenager," Tyler said, explaining that officials decided for a total replacement as opposed to building a companion bridge because the current span is simply too narrow for four lanes with shoulders for safety.

The current bridge will come down just as the new ones are going up — piece by piece. The bridge, once the longest box-girder bridge in the Western Hemisphere, will be sliced into pieces at the joints where it is built and removed, starting at the points furthest from the pillars supporting it.

Crews will then work toward the pillars and eventually remove them.

Building the bridges and tearing the current one down is hard enough, but crews will be doing it over one of the busiest shipping lanes in the country.

"I don't think switching the traffic (to the new bridge) is near as complex as the channel," said lead engineer Mike Perez, senior staff engineer for HCTRA.

At points when work is directly above the channel, regulations require ship traffic to cease. For businesses, that could disrupt operations, and make timing critical.

Toll authority officials, the contractors, U.S. Army Corps of Engineers, Port of Houston and Houston Pilots Association are all involved in discussions.

"We have been working with the pilots and port for four years," Tyler said. "We learned a lot about shipping."

The various stakeholders agreed to limit closings to two, three-hour closings during the daytime, with a five-hour gap between closings, during every 24-hour period. At night, crews can close the channel for nine hours, with a 48-hour period between closures.

The contract with Ship Channel Constructors allows for 42 closings for the southbound bridge, 42 closings for the northbound bridge and 33 for demolition of the existing bridge. The company has incentives to reduce the closings, with extra money available for every closing they can eliminate, down to 21 on each bridge.

Any closings in addition to those allotted cost the company money.

Morman said though complex, the new bridges are a huge boost for business around the ship channel and eastern Harris County.

"It is huge for the port," he said. "The extra capacity is coming as we know it is in demand. It seems like every year is a record year for the port."

The new bridge also helps keep traffic moving at highway speeds, eliminating a tight curve south of the bridge and reducing the steep 5 percent grade on both sides of the bridge that slow-climbing trucks and many cars.

Perez said the new bridges will have a 3 percent grade on the south side and a 4 percent grade on the north, which while not sounding like much, helps keep highway speeds constant.

Though the biggest single project for the county, the project cost is covered by toll revenues from the system and not taxpayer funds. County commissioners, acting as the executives of the toll road authority, approved the project.

"This is a great example of how well a toll system is designed to work," Morman said. "We would not be able to do projects like this if we had to wait on tax money."

?Though toll reliance by various local and state officials has rankled some drivers, Harris County's system remains one of the most financially healthy in the nation. The agency collected $774 million in toll revenue during its fiscal year that ended Feb. 28, 2017, a 2 percent increase over the previous year. As of last year, the agency had $1.32 billion not committed to any of its outstanding debt.

The $1.50 toll on the Ship Channel Bridge has not increased since the county toll authority took control from the defunct Texas Turnpike Authority in 1994. During other rate increases in 2007 and 2013, officials declined to increase the bridge price, saying it was already higher than others around the system.

Morman said he does not expect a rate hike due to this construction project, a welcome sign to some drivers.

"I feel like I've paid plenty," said Fred Miller, 56, who commutes via carpool across the bridge five days a week to his job at a chemical company. "Seems to me after close to 20 years, I've done my part. . But it'll be nice to have a new bridge."

Miller's mood dampened when he learned he'd have to wait years.

"Well, shucks, by then I hope I'm retired," he said of a 2024 opening day. "I'll come back to visit it, tell my grandkids 'I paid for that.'"

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Information from: Houston Chronicle, http://www.houstonchronicle.com