A system for securing a rail to a concrete railroad tie employing a two-piece insulator spacer that improves the resistance of the insulator spacer to the crushing deterioration induced by laterally-directed compressive forces during service. The insulator spacer comprises an upper member and a post member. The post member is subjected to high compressive loads in service and consists of composite material that is sufficiently electrically insulating to operably electrically insulate the rail with which the insulator spacer is in contact from the shoulder insert with which the improved insulator spacer is also in contact.