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By Major L. Jones, P.E., M.ASCE

Conducted as part of a unique public-private partnership, the recently completed $1.4-billion upgrade of a nearly 6.5 mi long section of Interstate 35W in Fort Worth helps reduce congestion along a busy transportation corridor. Part of the regional system known as the North Tarrant Express, the project adds managed toll lanes and expands and renovates existing highway infrastructure, all of which will be managed by a private entity for decades to come.

To be delivered in multiple phases, the North Tarrant Express (NTE) is a large-scale effort to improve mobility in North Texas by adding a regional system of managed toll lanes and revamping existing infrastructure along critical sections of key roadways. Earlier this year, construction wrapped up on a major component of the NTE, a nearly 6.5 mi long stretch of Interstate 35W in the Fort Worth area. Delivered by means of a unique public-private partnership (P3), the $1.4-billion effort known as the I-35W NTE Segment 3A Project was substantially completed several months ahead of schedule.

Running north and south through the American heartland, I-35 extends nearly the entire length of the contiguous United States and connects several major cities within the states of Minnesota, Iowa, Missouri, Kansas, Oklahoma, and Texas. As I-35 approaches the Dallas-Fort Worth metroplex, the highway splits into east and west segments, with I-35E heading to Dallas and I-35W going to Fort Worth. A major route for Fort Worth commuters as well as for regional, interstate, and international trade, this approximately 80 mi long stretch of I-35W includes several major interchanges at its intersections with such other interstate highways as I-820, I-30, and I-20.

The state of Texas and many of its major cities, including Dallas and Fort Worth, have experienced steady growth in recent decades. For some time, regional planning organizations and the Texas Department of Transportation (TxDOT) have planned to expand the I-35W corridor, which was primarily built during the 1960s and since has become the state's eighth most congested highway. However, the timing of such an upgrade would have to be coordinated carefully with other regional projects, and the project itself would have to be delivered creatively in order to maximize the final product.

Rebuilding a major interstate within a large city entails a great undertaking for a state department of transportation, the municipalities, residents, commuters, local businesses, contractors, and utility owners. By 2013, the approximately 6.5 mi long stretch of I-35W from I-30, near downtown Fort Worth, to its interchange with Interstate Loop 820 to the north (see map on pages 62 and 63) required an upgrade. The need for this project would lead to a comprehensive agreement in the form of a P3.

In March 2013, TxDOT signed a 52-year concession agreement with NTE Mobility Partners Segments 3 (NTEMP3), a company consisting of Cintra, the transportation infrastructure company that has its U.S. headquarters in Austin, Texas; Meridiam Infrastructure, the Paris-based investment and asset management firm; and the investment fund APG, of Heerlen, the Netherlands. Under the agreement, NTEMP3 would design, build, finance, operate, and maintain the stretch of I-35W corridor from near downtown Fort Worth to north of the interchange of I-35W and I-820. The scope of the project included constructing two managed lanes—known as TEXpress Lanes—in each direction, reconstructing general purpose lanes, reconstructing and adding frontage roads and bypass lanes, rebuilding cross streets at the overpasses and underpasses, and completely reconstructing the interchange of I-35W and I-820.

Separately, TxDOT oversaw the design and construction of a 3.6 mi long section of I-35W from north of I-820 to U.S. 81/287. Known as NTE Segment 3B, this project cost about $260 million and achieved substantial completion in December 2016. Together, Segments 3A and 3B added two managed lanes in each direction along a 10 mi section of I-35W while expanding and renovating the highway's existing facilities. The NTE also includes the addition of managed lanes and the reconstruction and expansion of 13 mi along I-820 and State Highway 121/183. Conducted in two segments, this $2.1-billion project was substantially completed in October 2014. Segment 1 extends from I-35W to where I-820 meets SH 121/183, while Segment 2 extends eastward to where SH 121 and SH 183 split. Additionally, plans are in the works for expanding and adding managed lanes to another 8 mi of I-35W as well as to other sections of I-820 and SH 183.

Getting the NTE Segment 3A project signed and approved as well as securing the financing were significant milestones. However, the true challenge of reconstructing a major thoroughfare had only begun. Before the start of construction, 140,000 to 145,000 vehicles were using the Segment 3A corridor on a daily basis. Therefore, planning and phasing would prove critical to ensure that the project continued to accommodate these high volumes of daily traffic while meeting its aggressive five-year schedule.

A $1.4-billion project does not get built by just one single entity. Like all megaprojects, the I-35W NTE Segment 3A Project had several stakeholders and major players that had different roles. The project owner, TxDOT, has executed several P3 projects throughout the state and has been a leader in defining large-scale, heavy civil projects that fit the mold to be delivered by means of the design/build/finance/ operate/maintain model.

As the project developer, NTEMP3 will oversee all facets of the project during the 52-year life of the concession. Cintra, the majority owner of the concession company, has worldwide experience in developing highway infrastructure and specializes in tollway and managed lane projects. The contractor, North Tarrant Infrastructure (NTI), comprises a joint venture of Ferrovial Agroman, which has its North American headquarters in Austin, and Webber, of The Woodlands, Texas. As subcontractors to NTI, multiple firms and compamaterials evaluation and testing, providing asphalt, manufacturing signs and structures, and telecommunication and illumination systems. For its part, NTI performed some work itself, including traffic control and the construction of certain bridge structures.

SAM-Construction Services LLC—a wholly owned subsidiary of Surveying and Mapping LLC, which has its headquarters in Austin—was selected by TxDOT and Cintra to be the independent engineer for the design/build phase of the I-35W NTE Segment 3A Project. In this role, SAM-Construction Services provided construction oversight, inspection, design and construction auditing for contract compliance, and engineering assistance from start to finish during the design/build phase.

CobbFendley & Associates Inc., which has its headquarters in Houston, and the engineering consulting firm Raba Kistner Inc., which has its headquarters in San Antonio, provided services pertaining to right-of-way (ROW) acquisition as subconsultants to NTEMP3. The facility agreement entered into by NTEMP3 and TxDOT outlined the ROW acquisition process for the developer to follow. Acquiring the more than 100 parcels needed for the project necessitated an immense level of coordination. Having two firms involved with this process proved critical to adhering to the project's aggressive schedule, which called for ROW acquisition, utility relocation, and design and construction to be completed within five years.

On a project of this magnitude, overlapping of activities is a must. Once the project was ready to break ground in May 2014, the first teams out of the gate addressed surveying, utilities, and ROW. In an unconventional but critical move, the developer assessed the status early on of the roughly 50-year-old roadways and bridges along the corridor. As the new caretaker of this infrastructure, NTEMP3 would now need to maintain the existing roadway and keep it intact until the completion of the new roadway. The assessment revealed what those close to the project, and anyone who had driven the corridor, already knew—the existing pavement, drainage elements, and bridges were failing in numerous locations. The status of the current infrastructure would require significant consideration during the early phases of construction, and the roadway would need to be monitored closely until traffic could be shifted to the new lanes.

Although TxDOT owned much of the ROW needed for the project, the footprint of the proposed highway improvements would affect 110 parcels. Complicating matters further, the agreement with TxDOT included an additional requirement regarding any parcels affected by what was called the necessary ROW, that is, the ROW required for reconstruction of the general highway lanes and frontage roads and the addition of the TEXpress Lanes. For such parcels, the acquisition process also would include the ROW needed for the ultimate buildout of the project, which eventually will add lane capacity to the corridor to accommodate future traffic demands.

This requirement added an element of complexity to the acquisition process, necessitating that the ROW team spend time and resources on land that would not affect the requirements of the immediate design/build process. From the developer's perspective, the goal of the team was to identify strategic locations that could be made available, sooner rather than later, to the contractor for early construction opportunities. A secondary goal entailed identifying parcels that might require long lead times to acquire, potentially disrupting the construction schedule.

Meanwhile, AECOM, which has its headquarters in Los Angeles, and OTHON INC., Consulting Engineers, of Houston, were selected by NTI to serve as the lead designers on the project. The design accounts totaled more than $78 million. AECOM was responsible for the project's north section, which extended from Fossil Creek Boulevard to 33rd Street and included the four-level flagship interchange at I-35W and I-820. With two flyover direct connectors constructed as part of the adjacent NTE Segment 1 managed lanes project, the final interchange, including the 10 direct connectors to be added as part of the Segment 3A project, would comprise 12 direct connectors linking the general purpose lanes of I-820 and I- 35W and the TEXpress Lanes of both highways. Although the finished product is impressive to behold, even more notable was the phasing of construction required to maintain connectivity of the existing facilities while moving more than 200,000 vehicles per day through just this one interchange in the project.

OTHON was responsible for the design of the south section, which extended from 33rd Street to near downtown Fort Worth. This section also posed challenges, including multiple gradeseparation bridges crossing over railroads. Of the eight railroad agreements required for the project, six were in the south section. This section also required four bridges over the West Fork of the Trinity River, to accommodate general purpose and managed lanes in both directions. The structures included prestressed-concrete girders having a maximum span of 145 ft.

Between the river crossings and railroad overpasses, more than 25 third parties were involved with reviewing and approving the designs, requiring a significant level of coordination. Because so many separate approvals affected the various stages of construction, the designers faced the challenge of addressing comments quickly and efficiently in order to obtain final approvals and keep construction on schedule.

With all the design approvals required before starting construction, the project team had to have a well-defined, efficient process for obtaining approved drawings. Per the contract, TxDOT and the independent engineer had 14 days to review a submittal and provide comments. Given the number of design packages that the project entailed, the parties could not always keep pace with the 14-day timeline. Weekly coordination meetings involving all parties enabled everyone to discuss pressing matters openly and set priorities for reviewing design packages. An electronic document management system was used to share information almost instantaneously, minimizing time lost to transit and helping keep the review process moving smoothly.

The topography and ground strata varied greatly within the 6.5 mi of the project. Some strata proved highly beneficial for the project in specific locations, while in other areas the shallow ground conditions presented challenges during construction. For example, shallow limestone rock near the I-35W and I-820 interchange obviated the need for deep drilled-shaft foundations. The shaft lengths needed for the tall, long direct-connector bridges within the interchange ranged from 11 ft to more than 40 ft, with most having depths of about 20 ft. The resulting shorter concrete placements reduced the opportunity for cold joints or other supply-related problems to develop. The smaller drilled shaft lengths also helped the team stay on schedule by reducing the overall time needed to drill and place bridge foundations.

Similarly, shallow limestone was found near the planned location of the pavement structure for the general purpose and managed lanes near the overpass at 28th Street, toward the northern portion of the south section. Upon this discovery, the design team used the large rock formation as part of the subgrade in place of the lime-stabilized soils that had been called for originally. As a result, the lime resources could be concentrated elsewhere in the project. Meanwhile, shallow rock material that had been excavated to lower the roadway grade where I-35W passes beneath 28th Street proved to be good material for use in embankments in the southern segment of the project. Slightly farther south, near the West Fork, some silty nonloadbearing materials, which were thought to be seams of previous riverbed settlements, proved useful for housing some relocated utilities and drainage pipes. Professional Service Industries Inc.—now Intertek-PSI, of Arlington Heights, Illinois—prepared the geotechnical report, which provided for substantial ground improvements in order to place the utility vaults, junction boxes for the drainage, and even some of the larger, deeper drainage pipes. Several of the rocks used for the ground improvements measured more than 18 in. across at their widest dimension.

As for stormwater runoff and drainage, nearly all the project's stormwater system consists of lateral and trunk line systems. Most of the outfalls drain to local creeks or existing trunk lines that were kept as part of the highway improvements. The design included two oil-water separators near the West Fork to ensure that the outfalls complied with local, state, and federal environmental requirements regarding discharges into the river.

Although environmental requirements did not affect the overall construction schedule, several environmental concerns had to be dealt with during construction. For example, devices for controlling erosion and sedimentation were installed during construction along the bank of the West Fork. Similarly, turbidity curtains were deployed in the river, and real-time surface water turbidity measurements were taken to monitor the water condition continually as part of the water quality monitoring program.

Because temporary material was added to the river to form peninsulas used for construction, a cost-effective, environmentally protective method for real-time monitoring was needed while the material was loaded into the waterway. To this end, turbidity monitoring was selected as the primary means of assessing whether construction activities resulted in the disturbance of river bottom sediments or the discharge of construction runoff into the river.

Turbidity change, in terms of Nephelometric turbidity units, was monitored on a real-time basis, and the data were transmitted via cellular modem to an off-site location and uploaded to a website in 15-minute intervals. In this way, water quality within the West Fork was monitored 24 hours a day, 7 days a week. In addition, two buoys containing the instruments were anchored in the river at locations upstream and downstream of the construction activities. These buoys transmitted the data from a sonde—a water quality monitoring device—to the host.

Furthermore, NTI had to assess the ongoing status of the freshwater native mussel population in order to contribute to their conservation before constructing bridges and temporary peninsulas in the West Fork. To protect mussel species from untoward effects associated with sediment entering the waterway, biological specialists from the lead environmental consultant—ACI Consulting, which has offices in Austin and Denver—removed the mollusks and relocated them upstream of the project site. In all, 33 native freshwater mussels were identified and relocated, while an additional 66 shell-only specimens were identified.

A freshwater mussel survey of the West Fork and another unnamed tributary of the Trinity River found no species listed as threatened or endangered at the state or federal level or designated by the state of Texas as a Species of Greatest Conservation Need. The latter is a list of native animals or plants considered to be declining or rare and thus in need of efforts to ensure their recovery.

One of the most innovative approaches used during construction involved an overhead conveyor system to transport massive amounts of excavated material from the west side of the project to the east side during a critical phase. The contractor developed the custom-made system by repurposing such available materials as steel forms used to make bridge straddle bent caps. The overhead system could be placed strategically, greatly helping facilitate the flow of traffic beneath it, and also proved less expensive and more conducive to the construction schedule compared with other alternatives. Hauling the material would have required full nightly closures and hiring large haul trucks to transport as much material as possible during the available closure period (between 9 p.m. and 5 a.m.) Not having to haul the material also eliminated the high potential for traffic and construction accidents, especially during nighttime work. For these reasons, the overhead conveyor saved time and improved project safety.

Reconstructing the complex interchange of I-35W and I-820 involved overcoming significant challenges. For example, finding and accessing the correct work area was a complicated endeavor for those working at the site. Imagine the difficulties faced by a concrete delivery driver attempting to find the correct location while access to the site is not clear and multiple, simultaneous concrete placements are under way. Against this backdrop, NTI's safety department developed a numerated, color-coded access map that originally started out as a means for emergency responders to find work areas if an incident were to occur in the work zone. This map concept evolved into what the quality and construction departments used as an accurate tool for locating and coordinating work, tests, inspections, and field meetings. As new construction areas became available and construction access points changed, the maps were updated accordingly and shared with the public relations department, which disseminated them to first responders. This innovative concept kept the entire interchange better organized and ultimately safer. The time spent by NTI's staff updating and optimizing these maps proved critical to ensuring the effi ciency of the construction schedule.

Whenever possible, NTEMP3 sought to improve the design, add value, decrease the project's life-cycle cost, reduce maintenance requirements, and improve quality. Initiatives implemented along these lines included the placement of certain safety devices in tight gore areas—that is, the areas between ramps and main roadways—or roadway locations with unforgiving geometry. Such devices included pylons, costefficient attenuators, and concrete barriers.

These safety devices sometimes were placed in potentially problematic areas. By identifying these areas and coordinating with the contractor to implement changes, NTEMP3 sought to improve the long-term performance of the roadway. For example, on the south section of the project, one northbound ramp that provides access to downtown Fort Worth contains a smallradius clover loop. The original design called for the use of a guard fence as the barrier along the perimeter. Recognizing the potential limitations of this approach, NTEMP3 upgraded the fence to a concrete barrier just before the ramp opened. In less than one week, the new barrier had been struck by a vehicle, but the concrete structure sustained no permanent damage. If the original design had been implemented, this outcome would have cost valuable dollars and resources to repair. In fact, such repairs might have been required frequently, while also resulting in the closure of the ramp each time they were necessary. Within one week, the implemented change paid for itself.

All Contractors aim to stay on schedule with every project, and Ferrovial Agroman, the majority stakeholder in the contractor joint venture, succeeded in these efforts.

The facility agreement called for the north section of the project—which extends north from the West Fork to the interchange of I-35W and I-820—to open in September. Ultimately, this stretch was opened five months early, in April.

The south section opened to traffic in July, also ahead of schedule. With this opening, Fort Worth and Tarrant County commuters have an extensive network of managed lanes that provide drivers options for their daily commute. With dynamic pricing that fluctuates with traffic to provide predictable drive times and a minimum speed of 50 mph, managed lanes are improving mobility in the region and helping address congestion in areas that historically have produced traffic jams even outside of peak-hour traffic.

Pending the completion in the first quarter of 2019 of two final connectors, the managed lanes along this section of I- 35W will boast a total of six entrance points. Five of those entrances are for northbound traffic, which currently can travel as far as U.S. 287, because of the previously completed NTE Segment 3B project. Combined, Segments 3A and 3B totaled $1.6 billion and extend for 10 mi. The managed lanes of Segment 3A also provide direct access to the eastbound managed lanes along I-820. In total, more than 23 mi of managed lanes have been constructed on I-820, SH 121/183, and I-35W.

Although some change-order work on the project remains to be completed, the I-35W corridor is reaping the benefits of the newly opened lanes. Direct connectors to Belknap and Weatherford Streets and the eastbound lanes of I-30 that were not a part of the original scope of work are still under construction. (These connectors provide direct access between I-35W and downtown Fort Worth, as well as between I-35W and I-30.)

In the meantime, traffic in the corridor is returning and city streets are experiencing less traffic. The ongoing maintenance and operation of the lanes includes a quick incident-response time to those who need roadside assistance within the limits of the corridor, and this helps keep traffic moving.

The overall upgrade of the I-35W project has been years in the making for this stretch near Fort Worth, and the fi nal product does not disappoint. The use of state-of-the-art technology to monitor traffic, observe real-time speeds, respond to incidents, and provide safer, more reliable options to drivers in the DFW area make the I-35W NTE Segments 3 Project one of the most advanced highways in the state of Texas.

Major L. Jones, P.E., M.ASCE, is the design and construction manager at NTE Mobility Partners Segments 3, for the I-35W project in Fort Worth, Texas.

Project Credits

Owner Texas Department of Transportation (TxDOT)
Project developer NTE Mobility Partners Segments 3, a concession company comprising Cintra, which has its U.S. headquarters in Austin, Texas; Meridiam Infrastructure, Paris; and APG, Heerlen, the Netherlands
Contractor North Tarrant Infrastructure, a joint venture of Ferrovial Agroman U.S. Corp., of Austin, and Webber, The Woodlands, Texas
Design, north section AECOM, Los Angeles
Design, south section OTHON INC., Consulting Engineers, Houston
Independent engineer for the design/build phase SAM-Construction Services LLC, a wholly owned subsidiary of Surveying and Mapping LLC, Austin
Right-of-way acquisition CobbFendley & Associates Inc., Houston, and Raba Kistner Inc., San Antonio
Adviser to the developer for design and construction KBR's Infrastructure Americas Division (now Stantec), Edmonton, Alberta, Canada, and Prointec, Madrid
Adviser, intelligent traffic systems and tolling Kilan Solutions, Plano, Texas
Technical adviser to the project's lenders and financers Mott MacDonald, Croydon, United Kingdom
Technical oversight and adviser to TxDOT during design and construction Jacobs, Dallas
Technical adviser to TxDOT for right-of-way and utilities Atkins, London
Geotechnical Professional Service Industries (now Intertek- PSI, Arlington Heights, Illinois)
Environmental consultants ACI Consulting, Austin and Denver (lead); Terracon, Olathe, Kansas; and American Underwater Services, Fort Worth, Texas

© ASCE, Civil Engineering, December, 2018


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