A 10 lane bridge, while still too big, would be preferable to the current 12 lane concept, and there are signs that a smaller bridge might become the new concept
One of the things that jumped out at me from the fact sheets I got at the recent Columbia River Crossing "open house", (last Wednesday), was a projection from a sheet titled, "Traffic Effects of 8, 10 and 12 Lane Scenarios." This sheet compares the "local streets impacted by I-5 backups" in a 10 lane and 12 lane bridge scenario. In the 12 lane scenario, of course, there are no local streets impacted by an I-5 backup, either in Portland or Vancouver.
But in the 10 lane scenario, there are six streets or highways that are impacted. All but one of them are in Vancouver. So this really is a Clark County thing. The new bridge must be as large as possible so drivers from the northernmost reaches of Clark County, and probably beyond, can get to Portland in time for...whatever.