A rail-support insulating device for electrically insulating a rapid transit rail and rail fastener from the rail support structure is described. The device includes an electrically non-conductive member that surrounds and extends outwardly from the rail fastener and over its support structure. Also a pair of planar disc members of similar material extend around and outwardly from the heads of the mounting bolts for the rail fastener, thereby forming long surface electrical creepage paths between the rail and the rail support that provide electrical isolation even when the entire assembly of rail fastener and rail support is wet with electrolyte.