One of the more challenging aspects of Sound Transit’s East Link Extension Project was placing a light rail track bridge system on the I-90 bridge, also known as the Homer M. Hadley Memorial Bridge floating across Lake Washington. This impressive 5,700-foot long bridge is made up of fixed concrete box girder segments supported by deep foundations, linked to a floating segment supported by 360-foot-long floating pontoons bolted together, along with transition segments connecting the fixed and floating segments. Full-scale testing was conducted by MxV Rail in the summer and fall of 2013, as a principal subcontractor on the project. Our team worked side-by-side at our Pueblo facility with Balfour Beatty Rail Infrastructure, Inc. which built a customized 5,000-foot test track, and Jesse Engineering in Tacoma, Washington, which fabricated two full-scale prototype track bridges. The prototypes went through extensive kinematic testing to make sure the sections were able to accommodate the range of movements that would result from the motion of the water underneath the floating pontoons. Four-car trains running at 55 mph traversed over the prototypes to test the performance of the track bridges. Together, the consulting and research teams confirmed that the proposed design met the track bridge system technical requirements, and the findings provided valuable new insights about fabrication, installation, adjustment and maintenance of the prototype track bridges. The $3.7 billion, 14-mile corridor of Sound Transit’s East Link Extension Project is on schedule to open in 2024.