Railway tunnels in North America, built decades ago, are generally in good condition but may need modifications for safety or new uses. Methods for modifying and rehabilitating these tunnels include converting single-track tunnels to double-track, improving clearance, and stabilizing structures with steel sets or shotcrete. Understanding original construction methods is crucial for planning effective remedial programs. The key focus is on minimizing disruptions to train traffic by using mobile equipment and completing work in small sections.