Track geometry I suspect, the point work will be on an adverse cant so higher speeds probably put excessive stress on them at high speeds so it limits it.
It's a simple problem to solve - put it back to 4-track and split it into 2x Derby and 2x Nuneaton with the dividing junction being as close to Landor St. as possible. The crazy thing is that Water Orton - Whitacre was the original route, the 'direct' line to Kingsbury being built in the early 20th century.
Thanks for the analysis. By the way did they ever use that rail control centre somewhere near Washwood Heath?
It's a simple problem to solve - put it back to 4-track and split it into 2x Derby and 2x Nuneaton with the dividing junction being as close to Landor St. as possible. The crazy thing is that Water Orton - Whitacre was the original route, the 'direct' line to Kingsbury being built in the early 20th century.