Challenge
The Arizona Department of Transportation (ADOT) decided to implement a multilane roundabout at the ramp terminal intersection between the Interstate 8 (I-8) westbound Exit 1 and the Harrold C Giss Parkway in order to maintain adequate traffic operations and improve safety for all roadway users. The intersection is tightly located between a Colorado River levee, an I-8 drainage pond, and multiple private commercial properties. The existing ramps have steep grades leading into the intersection area creating a challenge for the future large roundabout topography.
Solution
Keeping the project on schedule relied on establishing any additional right-of-way needs early in the preliminary engineering process. Kittelson used 3D modeling of the intersection area to identify the potential earthwork elements that could encroach on adjacent properties. Quick and precise iterations of the intersection model showed that constructing a retaining wall would minimize the need for new right-of-way and limit the acquisition process to one parcel. Kittelson used the 3D model in the final construction documentation phases to create detailed staking plans for the unique and extremely curvilinear roundabout geometry.
The Outcome
Tight Space, Big Roundabout
ADOT was able to secure the required right-of-way for the intersection reconstruction within the original project timeframe and reduce its costs of acquisition by completing a single transaction. The detailed roundabout digital terrain model was used by the contractor and construction surveyor to quickly lay out a set of complex geometry with multiple curves, raised islands, and drainage features. Electronically sealed plans in PDF format reduce the effort to create post-construction record drawings.
