A rail-support insulating device for electrically insulating rapid transit system rail apparatus from the rail support structure is described. The device includes a layer of electrically non-conductive material forming a boot that encloses the base of the rail where the rail passes over its support. This insulating boot extends upwardly on opposite sides of the rail web and outwardly therefrom to form long surface electrical creepage paths between the rail and the rail support that provide electrical isolation even when the entire assembly of rail, boot and rail support is wet with electrolyte.