A long-anticipated extension of the Katy Trail under Interstate 35E to the Design District and Trinity River is taking a giant step toward becoming a reality. Dallas' sports arena tax increment financing board is recommending using $11.5 million from its bond fund to make the $22 million project happen. A group promoting the plan has already raised $10 million in private donations. The so-called Hi-Line Connector would link the popular trail from its end point at Victory Park to the opposite side via an underpass. Advocates see it as a way to open the Trinity River area to additional mixed-use development.