Design-Build

OTHON served as the Lead Engineering Firm on the Grand Parkway Segment H and was responsible for the 23-mile design of SH99 from IH69 Interchange to US90A in Harris, Montgomery, and Liberty counties. This two-lane toll facility with intermittent four-lane sections will improve the connectivity within the 184-mile SH99/Grand Parkway loop, reducing congestions, providing an alternate route during emergency evacuations, and enhancing the overall movement of people and goods within the region.

Our team prepared design documents and drawings, including drainage design, SW3P design, structural design, Traffic Control Planning(TCP), roadway design, electrical, ITS/Tolling systems, alternative technical concepts, and bill of quantity for the construction of toll lanes within the project limits. We led the development of multiple separate constructions packages that included 52 bridge design packages, four traffic operations design packages, four SW3P design packages, four TCP design packages and four roadway design packages.

OTHON served as Prime Design Consultant and Lead Engineer for the southern section of the North Tarrant Express Segment 3A, a $450 million design-build project reconstructing 3.9 miles of IH 35W through one of the region’s busiest corridors. Designed and constructed concurrently to accelerate delivery, the project was completed ahead of schedule and recognized by ENR Texas & Louisiana as the “Best Highway/Bridge Project” in 2019.

OTHON provided full-service engineering, including roadway and bridge design (26 bridges), traffic control and staging, ITS and toll gantry design, signal and lighting systems, environmental mitigation, and utility coordination. Innovative solutions—such as eliminating a pedestrian bridge by rerouting access and optimizing traffic control phasing—helped reduce cost and construction time while improving safety and community connectivity.

By integrating advanced engineering, stakeholder coordination, and creative design strategies, OTHON helped deliver a transformative infrastructure project that enhances mobility, safety, and long-term resiliency in North Texas.

OTHON is serving as a key design consultant for the IH 35 NEX Central project, one of the most significant mobility investments in the San Antonio region. The project includes 9.5 miles of non-tolled improvements along IH 35, IH 410 North, and Loop 1604, spanning the cities of San Antonio, Live Oak, Selma, and Schertz in Bexar and Guadalupe Counties.

OTHON is leading the detailed design of approximately 5 miles of improvements, including reconstruction of the IH 35/Loop 1604 interchange, elevated mainlane viaducts, ramp and frontage road upgrades, and Loop 1604 geometric enhancements. Our scope also includes driveway and sidewalk reconstruction, park-and-ride facility improvements, and pavement rehabilitation.

In addition, OTHON is providing Maintenance of Traffic (MOT) design services across the full corridor to ensure safe and efficient operations during construction. Through our leadership in complex interchange and roadway design, OTHON is helping TxDOT deliver long-term mobility, safety, and connectivity solutions for the rapidly growing San Antonio metro area.

OTHON served as Lead Design Firm for the 7.5-mile reconstruction of SH 121/SH 183 from IH 820 to Industrial Boulevard, a high-volume corridor carrying approximately 280,000 vehicles per day. The project included nine grade-separated intersections, a directional interchange, braided ramps, 40 bridges, and seven major FEMA stream crossings.

OTHON delivered full multi-discipline PS&E, covering roadway, bridge, drainage, traffic control, ITS, tolling, utilities, environmental mitigation, and ADA-compliant pedestrian facilities. A corridor-wide Traffic Control Plan was developed to maintain traffic flow across five major phases, including an accelerated pedestrian overpass at Cavender Drive to improve safety and accessibility.

Through design optimization and constructability reviews, OTHON reduced elevated viaducts to grade, eliminated 300,000 sf of retaining wall, and cut bridge deck area by 40%—saving approximately $100 million and contributing to a final construction cost of $700 million. The project earned multiple awards, including ENR’s Best Highway/Bridge and Best Safety Project, and AASHTO’s America’s Transportation Award for budget efficiency.

OTHON served as Lead Design Engineer for the $450 million North Tarrant Express Segment 3C design-build project, reconstructing 7.3 miles of IH 35W from North Tarrant Parkway to Eagle Parkway, including the IH 35W/SH 170 Interchange. The project expanded corridor capacity with new managed toll lanes, auxiliary lanes, and continuous frontage roads, while accommodating future general-purpose lane additions.

To optimize cost and efficiency, OTHON performed structural evaluations to reuse existing bridge-class culverts, designed overhead sign structures, and delivered ITS, tolling, illumination, and signal systems. A hybrid lighting solution was implemented to meet standards and minimize airspace impacts near Perot Field Fort Worth Alliance Airport.

The project reached substantial completion in June 2023—three months ahead of schedule—enhancing mobility, safety, and connectivity along this critical corridor.

OTHON served as Lead Design Engineer for Segments A1 and L1 of California High-Speed Rail Construction Package 4 (CP 4), a $444 million design-build project spanning 22 miles through the Central Valley. The segment includes 12.46 miles of new high-speed rail alignment designed for speeds up to 250 mph, along with embankments, viaducts, aerial structures, and relocation of four miles of BNSF track.

OTHON provided comprehensive civil and structural engineering services, including trackway and roadway design, post-tensioned concrete bridges, canal crossings, and utility coordination with agencies such as BNSF, Amtrak, CALTRANS, and Kern County. We also supported systems integration, environmental mitigation, and ROW adjustments.

Completed on an expedited five-month design schedule, the project incorporated alternative technical concepts to enhance constructability and resiliency. OTHON’s leadership helped deliver a fully grade-separated alignment that supports future high-speed operations while reducing costs, mitigating risks, and adding long-term value.