The goal of this $95 million urban interchange reconstruction project was to alleviate the poor conditions and geometric concerns associated with six existing ramps and mainline structures in the area. Nearly 60 years old, those structures were determined to be structurally deficient and/or functionally obsolete. When coupled with peak traffic volumes, the crash rates would turn out to be considerably higher compared to the statewide average for interstates.
One major component of the I-280/Route 21 Interchange Improvement project was to address longstanding concerns regarding the safety and efficiency of the interchange. “You’ve got some of the existing connections between I-280 that were leading the state into a local roadway network, which is not a standard design anymore because it presented an unsafe condition,” Mike Sidani, senior vice president on the project for Michael Baker, told Roads & Bridges. Sidani explained that the team reduced the number of ramps to get on and off the interstate in order to curb the conditions that would occur when stopped vehicles would have to travel from zero miles per hour up to the speed limit as they entered the interstate, which would typically cause safety issues and traffic disruptions. “Three additional movements were added from the local network up to the I-280 highway using current standard designs, which is an improved design. Some of the safety improvements were that the existing design involved a number of different successive on- and off-ramps onto I-280, which was a major safety issue because some of these ramps dealt with having some stop conditions, which is unsafe for traffic to access the interstate highway. So these conditions were eliminated, and instead the new design provided free-flowing ramp connections.”
Since the impact to historical structures along the project footprint was a concern, designer Michael Baker International prioritized keeping vibrations to a minimum by incorporating vibration monitoring and control procedures in the project specifications. During construction, the surrounding structures were analyzed to collect displacement and vibration data. When needed, construction would be stopped to address vibrations. To address the major concern regarding vibrations coming from the I-280 pier column foundation, the team came up with an innovative solution to strengthen the existing footing with post-tensioning and pin piles to reduce the vibrations. Since the pier column foundation was located less than 30 ft from the Plume House, this solution was designed to protect the building and other nearby structures. The plan worked out, and no facilities were impacted during construction.
