[UPDATE October 19, 2013 - It semi-officially opened today and is open for riding.]
From the west side you can walk the trail, under the highway bridge.
Here's what this looked like in 2007.]
When the State does a project, they tend to obliterate the landscape and then build it back up from scratch. I'm sure they have good reasons for it. In this case the bridge has been expanded greatly. Before there was just a little edge along the path under a bridge you had to duck to get under in spots. Now the space next to the creek is bigger, it seems, than the creek.
Here's what this spot looked like in May 2012:
And here's going under the bridge the other day:
And near the same spot in 2008. This was the whole trail then right against the water. And when the creek was really high, the whole trail was gone. The heavy equipment is between me and the water above - also the orange fencing is along the water. And the bridges were shorter and lower.
And here's what that used to look like:
Once you get out from under the highway, instead of the one-bike winding path through the fireweed, there's more bike superhighway up to this bridge which is blocked for now. At the right times, you can watch the spawning salmon from this bridge. We're very close to The Wild Berry tourist trap at this point, just west of the Seward Highway (see map below).
Getting to this bridge used to look like this:
Turning around at this point, it now looks like this:
One more picture of the bridges - now looking east from the west side.
And here's a map for the area. I started on the east and went to the west, then turned around and went back where the wooden bridge was blocked off.
When this is done, you'll be able to ride from downtown out to Westchester Lagoon up the Chester Creek trail to Goose Lake and the the University crossing either over or under all streets via tunnels and bridges. At the university you have to cross a parking lot and a few streets to get to the bridge at Tudor and Bragaw (now Elmore), and then on the Campbell Creek bike trail. There's a bit of a break in the trail at Lake Otis, but then you get back on a wooded trail that will go under the Seward Highway and then on to just past Victor near Dimond coming out at Dimond High School. Then there zigging and zagging through neighborhoods to connect to the trail in Kincaid park, and from there you can get back downtown.
The Trails of Anchorage site says it's 13 miles from Kincaid Chalet to Goose Lake, and I'm guessing it's not much less for the rest of the loop I described.
Here's a link to the Arctic Bicycle Club.