The long trains roll

A book from the World War Two period, about railroading through the mountains of the east during the war, with a Nazi sabotage attempt thwarted by young protagonists. YA classification. The railroad is pretty clearly the Pennsylvania, though it is never named. Emphasis on war-time traffic, including troop trains, trains of military equipment and oil tanker trains, as well as the "normal" passenger and freight traffic. Setting c.1942-44.