WASHINGTON — Metro said Friday that its massive effort to improve safety on the rails has reached a milestone.

At underground station platforms throughout the Metrorail system, all porcelain insulators have been replaced with fiberglass versions that are more heat-resistant.

Metro General Manager Paul Wiedefeld sped up efforts to swap out insulators at those locations after an arcing insulator at Federal Center Southwest Station on May 5 sparked a fire. An arcing insulator fire near McPherson Square Station shut down the entire system for more than 24 hours for emergency inspections and repairs in March.

The insulators are installed about every 10 feet along Metro’s 230-plus miles of track.

Metro’s 10-month-long repair plan calls for replacing 12,000 insulators. The massive rehabilitation project is intended to address years of deferred maintenance.