The Oregon Department of Transportation is asking federal authorities to suspend unit oil trains from going through the Gorge and the state until more is known about the cause of the derailment in Mosier two weeks ago.  Officials made public a letter from ODOT Rail and Public Transit Division Administrator Hal Gard to Federal Rail Administration Regional Administrator Mark Daniels asking for the moratorium during a Hood River meeting on Thursday.  The letter expresses concern with lag bolts, a type of fastener used on curved sections of track to attach the rail to the rail tie, and requests that oil train traffic not resume until a means of detecting defects with those bolts is developed.  Union Pacific has indicated a failure of the bolts cause the June 3 derailment.