Modern road construction projects demand precision, speed, and cost efficiency. On the I-84 Baldock Slough South Baker Interchange project in Baker City, Oregon, the general contractor Oregon Mainline Paving demonstrated how advanced machine control technology can transform a complex milling and repaving operation. By integrating Trimble 3D milling systems with a Wirtgen W2100 cold milling machine, the company completed the 19-mile project in one year instead of the scheduled two and cut labor hours, machine time, and overall costs by 50 percent. This case study examines the technologies, methods, and project management strategies that made these results possible. For a broader look at how modern Asphalt and Concrete Paving Equipment Machine Technology Construction methods support large-scale projects, this article provides essential context.
Project Scope and Milling Challenges on I-84
The Baldock Slough South Baker Interchange Project
The Oregon Department of Transportation awarded Oregon Mainline Paving a $17,949,200 contract to mill and repave 19 miles of I-84 in eastern Oregon. The roadway consisted of two eastbound and two westbound lanes along a historic stretch originally part of the Oregon Trail. The project called for 66,582 cubic yards of grinding and involved 135,000 tons of ground asphalt. The finished pavement used 62,000 tons of new asphalt and 154,000 square yards of nine-inch-thick concrete.
Variable Depth Milling Across Four Lane Profiles
The most significant challenge was the complex cross-section design. ODOT specified different surface types and depths for each lane, requiring the milling crew to grind at four distinct depths across a 42-foot-wide roadway:
| Lane Section | Width | Milling Depth | Surface Type |
|---|---|---|---|
| Fast lane shoulder | 6 feet | 0 to 2 inches | Asphalt |
| Fast travel lane | 12 feet | 2 to 4 inches | Asphalt |
| Slow travel lane | 14 feet | 8 to 10 inches (up to 12 inches on bridges) | Concrete |
| Slow lane shoulder | 10 feet | 3 inches | Asphalt |
Jim Swenson, licensed professional land surveyor for Oregon Mainline Paving, explained that the crew milled from shallower to deeper sections to avoid leaving ground asphalt behind. The grinder used a 7-foot 2-inch drum and required nine passes across the roadbed. Seven passes would have sufficed for most sections, but two additional passes were needed in the nine-inch-deep concrete lane section.
Why Traditional Stringline Methods Were Not Practical
Conventional milling projects rely on stringlines and manual grade checking to control cutting depth. On a project with four different depth transitions across the same cross-section, setting and maintaining stringlines for each pass would have been prohibitively time-consuming. The variable slope requirements and the need to match existing surface profiles without cutting into subgrade made automated machine control the only viable approach.
Machine Control Technology for Precision Milling
Trimble 3D Milling System on the Wirtgen W2100
Oregon Mainline Paving purchased a new Wirtgen W2100 cold milling machine and worked with SITECH Oregon in Portland to equip it with a Trimble GCS900 Grade Control System paired with an SPS930 Universal Total Station. This combination enabled the crew to mill surfaces at variable depth and slope without relying on any stringlines. The robotic total station tracked the milling machine in real time, adjusting cutting depth based on the 3D design model.
From ODOT Design Data to a Usable 3D Model
ODOT provided site model and design information, which SITECH Oregon converted into a functional 3D model using Business Center-HCE software. This data preparation step was critical. The 3D model contained the exact surface elevations, slope transitions, and depth offsets for each lane so that the machine control system could follow the design automatically. The system minimized over-cutting, produced a smoother milled surface, and reduced the amount of asphalt or concrete required during repaving.
Grade Control on Earthmoving Equipment
Machine control was not limited to the milling operation. During Stage I, dozers equipped with dual-mast Trimble GCS900 Grade Control Systems and GPS RTK equipment performed the earthwork for temporary crossovers. The crossovers required stone embankment placed two feet below existing ground, with geotextile fabric underneath, then brought to grade and paved. The GPS-guided dozers ensured each crossover met the precise elevation requirements without manual staking.
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Phased Execution: Stage I and Stage II Timelines
Stage I: Crossover Construction (March to April 20)
Stage I involved constructing crossovers at the ends of the project and at three interchanges spanning the 100-foot-wide earthen median. Traffic was routed onto the eastbound side in both directions. At the southern incline, the crew built an additional temporary passing lane. Key activities included:
- Stone embankment placement two feet below existing ground with geotextile fabric underlayment
- Grading and compaction using GPS-guided dozers
- Paving the crossover surfaces to match final roadway elevation
- Completing all crossover tie-ins before the July 4 deadline
Stage I work began in March and was finished by April 20, well ahead of the July 4 milestone ODOT had set.
Stage II: Eastbound Milling and Paving (April to August)
Stage II grinding of the eastbound freeway began April 21 and was completed May 18, except where interchange traffic crossed the existing surface. At each interchange, the team built two crossovers per on and off ramp so traffic could be switched onto the poured concrete lane after curing. The blockout was then ground and white paved.
Once white paving was finished, the remainder of the eastbound side was paved. Traffic was switched back to the Stage I configuration, the crossovers were removed and rebuilt to accommodate westbound traffic crossing the under-construction eastbound side. All of this work had to be complete by July 4.
Westbound Milling and Final Paving (July to September)
Grinding of the westbound freeway began July 6. The crew finished the 9.5 miles in 24 grinding days, completing the work on August 9. Concrete and asphalt were placed using Blaw Knox 220 and 5510 pavers. Oregon Mainline Paving easily met the September 30 top-lift paving cutoff date set by ODOT. Other items completed during this phase included:
- Sleeper slab and concrete anchor construction
- Guardrail and barrier installation along the new roadway profile
- Pavement striping and signage for the reopened lanes
- Final grade verification and surface tolerance checks
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Measurable Results and Industry Takeaways
IRI Scores and Tolerance Compliance
Oregon requires an International Roughness Index score of 45 for new pavement. Oregon Mainline Paving achieved a score of 35, significantly below the maximum. ODOT also enforces a zero-out-of-tolerance policy for concrete depth, with random measurements taken within every 200-foot section. The concrete subcontractor had estimated a three percent material overrun, but the actual overrun was only one percent, thanks to the accuracy of the milled surface.
Cost and Schedule Performance
| Performance Metric | Planned Baseline | Actual Result | Improvement |
|---|---|---|---|
| Project schedule | 24 months | 12 months | 50% faster |
| Worker hours | Baseline estimate | 50% reduction | 50% less |
| Machine time | Baseline estimate | 50% reduction | 50% less |
| Project costs | Baseline estimate | 50% reduction | 50% less |
| IRI score | 45 (max allowed) | 35 | 22% smoother |
| Concrete overrun | 3% estimated | 1% actual | 67% less waste |
Swenson noted that this was the company first project using a robotic total station with machine control. The milling crew ground 9.5 miles of highway in 24 days, making nine passes across the full road width each time and maintaining a vertical tolerance of 0.02 feet throughout.
Key Lessons for Paving Contractors
The Oregon Mainline Paving project demonstrates several principles that apply to any large-scale milling and repaving operation:
- Invest in machine control early. The Trimble system paid for itself through reduced material waste, faster production, and lower labor costs on the first project alone.
- Partner with a qualified dealer. SITECH Oregon converted the ODOT design data into a production-ready 3D model, eliminating guesswork in the field.
- Plan milling sequence around depth transitions. Milling from shallow to deep sections prevented leaving loose ground asphalt and reduced cleanup time between passes.
- Use technology for quality control. Accurate milling directly improved IRI scores and concrete placement tolerances, which translated into higher pay factors.
- Set aggressive but achievable milestones. The July 4 deadline for Stage I work created a clear target that focused the entire crew.
Crews looking to improve their milling accuracy and overall job site productivity can study how Essential Paving Equipment and Technology for High Efficiency road construction crews combine modern machinery with digital work flows to deliver consistent results.
Conclusion
The I-84 Baldock Slough South Baker Interchange project shows that machine control technology is not just a convenience for large milling projects. It is a strategic investment that can cut project timelines in half, improve pavement quality, and reduce material waste. Oregon Mainline Paving finished a two-year contract in one year by combining hard work with the right technology, proving that 3D milling systems deliver measurable returns on even the most complex roadway profiles.