Wikipedia is saying The Konkan Rail route from Roha to Mangaluru Jn. only 324 kms out of the 757 kms long line can be doubled. Rest 433 kms fall in challenging mountainous terrain/zone. 324 kms of Konkan Railway runs on plain line, of which 46 kms between Roha & Veer already doubled. So here are the stats: -
Line length = 832 kms from Panvel to Mangaluru Jn.
Doubling done = 121 kms from Panvel to Veer.
Doubling...
more... left = 203 kms more in Honnavar-Mangaluru & Madure-Vaibhavwadi Road.
Survey for Doubling of the challenging 433 kms is going on as on 2022-23.