Who: El Dorado County, Calif., DOT
Total Area: 1,788 square miles
Roadway Miles: 1,100 miles
Traditionally, the concept of building information modeling (BIM) has been applied to buildings. But it can be applied to all things built, horizontal and vertical.
In highway engineering, the model acts as a repository and source of project information. Planners, engineers, contractors, and owners use it throughout an asset's entire lifecycle — from conceptual design, detailed design, and construction to operations, maintenance, and asset management — to access coordinated, consistent data that can be continuously improved in quality and detail. Information isn't translated or watered down; it's simply created, updated, and used to improve downstream data quality.
Because they can visualize a project at any stage in the design process, transportation engineers minimize change orders by identifying problems far earlier, when they can be corrected much more easily and less expensively. Using a realistic model means engineers can run multiple design scenarios and quickly see the impact of each on project costs and timelines.
To understand how the modeling concept applies to highway engineering, it's important to identify what functions create, update, or pass data to other functions. This defines the overall hierarchy and helps identify techniques to streamline processes.
Take the example of a task performed in conceptual design: selecting a corridor that minimizes environmental impacts to agricultural land.
If we break down the activity, a number of problems are immediately apparent. First, the data needed to make sound engineering decisions is segregated by the way it's stored, by the way it's used, by the organizations that own it, and by the technology that can use it.
Information modeling integrates the relationship between parcels of land and the roadway geometry so that when one piece of data, such as the proposed centerline of the roadway, is modified a related piece of data — land area — is likewise affected. The modeling process uses data holistically to investigate and evaluate design alternatives and determine the need for things such as Agricultural Impact Statements in conceptual design.
The process enables stakeholders to streamline functions performed in other phases of the transportation engineering lifecycle as well. For example, data created, used, or updated in design is used and updated in construction. This as-built data is invaluable for operations and maintenance, inventory management systems, and asset management systems. To complete the lifecycle, this same data is used again in the next cycle, which begins with conceptual design, to assess impacts and eliminate the need to ‘recollect' or recreate data.
El Dorado County recently experienced the process for the first time.
Bordered by Sacramento County to the west and Nevada to the east, the county lies in east-central California. It's highly diverse, comprising a variety of towns and cities such as South Lake Tahoe and Placerville, the expanding Sacramento suburbs, parklands, and the Sierra Nevada Mountains.
One area, Cameron Park, was once a rural town but is rapidly evolving into a more suburban center. As growth continues, the county works to ensure roads keep up with the demands placed on them by increased capacity.
One intersection in particular presented a unique design challenge. To accommodate adjacent commercial and residential development, an increasingly busy roadway was scheduled to be widened and signalized.
The deadline for meeting the construction season was quickly approaching when it was deemed necessary to incorporate additional grading, utility, and structural work into the intersection project. The original bid set plans existed only in hard copy, so evaluating the feasibility of incorporating the revisions would take weeks, even months.
To avoid losing an entire construction season, engineers used the challenge to break in their newly acquired 3D design and analysis software, Autodesk's AutoCAD Civil 3D.
They built a 3D model of the roadway corridor that replicated what was represented in the original, two-dimensional design. Using the model they were able to see the impact of proposed modifications to right-of-way boundaries, trees, and existing utilities and adjust horizontal and vertical alignments to meet specifications.
Because the model is dynamic, modifications to the alignment or profile instantly updated the corridor and its associated daylight lines. As a result, the impacts of the changes were readily apparent, allowing the team to use as much of the available right of way as possible, avoid environmental issues, and clear existing utilities.
For example, to evaluate different utility configurations it was first necessary to determine the impacts of the grading each configuration would require.
“The analysis turned weeks of work into three or four hours to analyze the impacts of three different grading alternatives and utility alignments,” says Principal Engineering Technician Steven McVey. “It was just a matter of dragging the alignment and profile until the design was optimized.”
The feasibility study was finished and the project poised to go out for bid when a local utility requested a study of where additional electrical poles should be placed around the intersection — one of those last-minute requests that throw projects completely off schedule. In addition to the study itself, the utility work had to be completed before the county could begin construction on the intersection.
McVey's team needed to locate the poles and guy anchors as far as possible from the road modifications while also avoiding adjacent privately owned property. The poles also needed to be placed at an ultimate grade, which would require excavating approximately 25 vertical feet of the adjacent hillside. To visualize the potential impact to the surrounding area and right of way, the horizontal and vertical locations of the poles and guy anchors were critical. At one point, the department shared CAD files with the utility.
Using the same model that was created during the design phase, the team placed “virtual poles” at different grades in various locations to determine where the necessary clearance from the surrounding hillside could be achieved.
“The modifications were delineated by utilizing the automated labeling features,” says McVey. “By selecting the desired label style and setting the design alignment current, the stations and offsets of key points were labeled with a click. All of the plan and profile labeling styles are dynamic and annotative, allowing them to automatically adjust to the rotation and scale of the sheets. This ability expedited the drafting of the plans tremendously.”
The additional modifications were incorporated into the plans and the intersection improvements were sent out to bid on time, keeping the project and adjacent development on schedule while giving El Dorado's engineers their first complete “transportation systems” perspective.
— Weiss (firstname.lastname@example.org) is market readiness manager, transportation engineering for Autodesk Inc. Special thanks to Steven McVey of the El Dorado DOT for his contributions to this article.