The big dig and putting I-80 through Sugar House underground are drastically different projects. The Sugar House project would be a simple cap, yes I realize it's not "simple" but it is simple in comparison to the Big Dig. Placing a cap on the area near Sugar House park wouldn't require any wear near the engineering, time or money that even a similar length of the big dig cost. Even a simple half mile or several hundred yards of a cap would do a lot to connect the Highland Park neighborhood to Sugar House park. The cap below wouldn't require any additional depth, and a small amount of ventilation. It is only about 600 yards long.
You could put limited access to just the south side of the park and ad a ball field, and one small parking lot (possibly. I realize this is residential and that could be a hard sell), but either way you could add some paved paths from the Highland Park neighborhood that connect into the remainder of the park. Imagine how many more people they could accommodate for 4th of July fireworks.
