A commission that's studying ideas to reduce heavy traffic between Eau Claire and Minneapolis has ruled out a commuter rail line between those two cities. The Gateway Corridor Commission voted yesterday to eliminate a 99-mile train as an alternative for easing congestion along Interstate-94. The panel has seven other ideas to consider. One of them is a 420-million-dollar rapid transit bus line that would follow the path of the Interstate. It was among the highest-rated options by the consulting firm of C-H-Two-M, which has spent a year-and-a-half looking at the various proposals. The firm rated the commuter rail line as among the least desirable. It would have cost about one-and-a-quarter billion dollars.