What is the fine-grained topic of the following text: "The railroad is a 1,520mm (4'8½") standard gauge" The statement should read "The railroad is a 1,520mm (4'11 5⁄6") russian gauge"
"The railroad is a 1,520mm (4'8½") standard gauge with passing loops at every 20km (12 miles.)" Only return the topic.
Railroad Gauge Specifications