Better Freeways by Design
Innovative use of 3D engineering and design software keeps a major freeway interchange project on track in Washington state.
Clark County was responsible for designing and constructing local roads and other elements that would serve the freeway interchange. WSDOT’s primary responsibility was designing and managing construction of the new interchange that would extend NE 139th Street across the freeways and build two on-ramps to I-5 and one off-ramp from the freeway.
The project was financed largely with outside grants and loans, including $84.3 million in state revenues from the Washington Legislature’s 2003 decision to add 5 cents to the gas tax.
Clark County faced strict deadlines because funding was tied to specific construction seasons. The county needed to have its portion of the project built before WSDOT could begin construction on the new interchange. Delays by either the county or its contractors would jeopardize the overall project. Comprehensive planning, along with realistic modeling and simulation, was essential.
The county was already designing roads to serve the new interchange when it purchased Autodesk AutoCAD Civil 3D software. According to Bruce Klug, PE, a county engineer who worked extensively on the east side of the interchange project, the decision to switch from the old design software proved critical in meeting project deadlines.
Early in the project, groundwater issues required the original design to be scuttled. A planned tunnel under the two freeways was abandoned in favor of a bridge. With the Autodesk software and other technology, county engineers were able to quickly adapt and completely redesign county roads on both sides of the interchange.
Engineers initially changed the road profile and raised it at a 5 percent grade to match the freeway bridge while still constructing an intersection at the bottom of the hill east of the freeway. This change also required several walls to be added to the project. By using AutoCAD Civil 3D, the county was able to dramatically reduce the time necessary for this major design change. Because of the nature of the software, county engineers didn’t have to “chase” different datasets for design synchronization.
“In our old software, if we had a horizontal or vertical change, we would have had to reprocess each section of roadway separately in multiple files and update the surfaces and terrain models,” Klug explains. “In Civil 3D, we use data shortcuts. Any change to the design is automatically updated in any profiles that are being referenced off the surface, as well as all the surface models. The surface models, in turn, update our stormwater design, including details such as rim elevations on the manholes. As a result, everyone on the project team is seamlessly working on the most current design at every stage.”
Survey data was easily added to the model, along with data from three other sources provided by WSDOT. The ability to pull multiple datasets into a single model reduced the amount of fieldwork required for the project. “There were probably hundreds of drawings that all referenced this one ground model that had multiple sources brought into it to create a Civil 3D surface,” Klug says.
The county created a 3D corridor model that included the critical intersection at the bottom of the hill. By having a dynamic corridor, the county determined that it would have problems meeting Americans with Disabilities Act (ADA) requirements for crosswalk slopes.
The software allowed the county to adjust curb and centerline profiles for ADA compliance and “see” how those adjustments affected the entire corridor. This dynamic process was a huge improvement over previous design techniques. “Whether we were looking at existing ground surface models and shading them, or looking at them in a three-dimensional view to identify busts or errors in the topo, that ability was seamless in Civil 3D,” Klug says. “The ability to quickly look at the true design was a big advantage.”
The county also used AutoCAD Civil 3D to design a drainage system that navigated through layers of utility pipes and lines, including 6-inch and 8-inch high-pressure gas lines a 12-inch water line, a major fiber optic line, gravity and force main sanitary sewer lines, and several storm lines up to 48 inches in diameter.
By using AutoCAD Civil 3D, Clark County quickly discovered that its storm design would create major conflicts with existing utilities. Specifically, the county would not have been able to get over the fiber optic lines without taking out the large high-pressure gas lines.
Both lines would be extremely expensive to relocate and, more importantly, would have created significant delays. The fiber optic line operator said it would take nine months or longer and cost $1 million to relocate the line. To complicate matters further, the storm outfall’s location was fixed because it connected to a pump station and pond that WSDOT designed.
Having everything tied together in a 3D model allowed the county to rapidly redesign the entire drainage system around these key elements. Without the software, the county would have been forced to take a more piecemeal approach that would have resulted in delays and additional costs. “In our old software, changing an alignment or profile was a completely disconnected process,” Klug says. “Having the data shortcuts and the ability to link everything together with automatic updates was a big advantage.”
Once the county had redesigned the storm network, it still was left with a complicated installation for its contractor. The county used the 3D software to produce dynamic cross-sections of all utilities so the contractor could see both existing and new pipes. This allowed for improved construction planning and coordination. For example, a representative from the gas company needed to be present whenever construction was within 2 feet of high-pressure gas lines. Having this type of information available and accessible for the contractor expedited construction and saved time and money.
Another benefit that sounds simple but has had significant impacts on past projects is determining the lid rotation on manholes during design. The county has encountered problems when manholes were installed with the manhole lid in the wheel path of traveling vehicles, which can become a noisy disturbance and a point of contention in urban settings. The problem is exacerbated when lids cannot be rotated during construction because ladder rungs are cast in the manhole prior to shipping to the construction site. In response, the county produced detailed plans that showed proper rotation of the lids for traveling vehicles and ensured that ladder placement will not conflict with connected pipes.
Clark County has received several accolades for its use of Autodesk software. In 2012, the county won second place in the inaugural Autodesk Excellence in Infrastructure Competition after a panel of industry experts evaluated 44 nominations for transportation, urban planning, energy and water/wastewater projects in the United States and overseas.
The county’s use of AutoCAD Civil 3D software also is being recognized by its peers in Washington. In early 2013, the Washington State County Road Administration Board passed a resolution honoring the county for its work. The board recognized Klug as a leader in the applications of AutoCAD Civil 3D software, which is used by most of Washington’s 39 counties. Klug, the board concluded, had “distinguished himself as an expert in the discipline of civil engineering design and in the use of civil engineering design software.”
Clark County has begun incorporating 3D plans into its property negotiations and open house events to convey the potential impact of construction designs with the public in a visual, easy-to-understand format. The software has also improved the overall decision-making process. “Now we’re creating multiple alternatives for every project because we can create 3D models much faster,” Klug says. “It’s a better way of approaching design. We’re stewards of the public money, so we need to make sure we’re doing the right thing and implementing the best design through the most cost-effective process.”
Klug says the 3D models provide another benefit as well. As area contractors have adopted GPS machine control technologies, they are able to pull in the AutoCAD Civil 3D models from Clark County, which substantially reduces the amount of survey fieldwork required in the construction phase. Instead, surveyors are being relied on for their data management expertise.
As for the Salmon Creek Interchange Project, Clark County finished major construction on its portion of the project in late 2011. WSDOT awarded a contract to build the interchange in summer 2012.
In March 2013, the state’s contractor started placing the first of more than 100 63-ton concrete girders on the previously installed piers that will provide the foundation for the freeway interchange. Work will continue throughout the year, with the overall project scheduled for completion in 2014.
“This project demonstrates how Clark County uses technology to design roads and other infrastructure quickly, nimbly and with greater precision and efficiency,” Klug says.