Quadrupling of rail lines only exists for about 50-60kms around the major metros.
On trunk routes on the Golden quad, some routes are not even doubled and not electrified, like Chennai-Mumbai where there is a large stretch between Bhigwan and Gulbarga where about 100km is not doubled and certainly all of Bhigwan-Solapur-Gulbarga not electrified. However a tender has been issued to Tata to electrify this section in the last month and now electrification and doubling will go on together. By the end of May about 70km will be left for doubling.
CCEA had cleared many sections for third lining between Chennai and New Delhi in 2015, but the pace is slow and there is no guarantee that by 2025 the project will be complete. Funds are not forthcoming and various railway zones have different efficiencies. SCR is one of the better performing zones and they too are not on top as there is a paucity of funds. Concentrating on this North-South link let us see what we have:
New-Delhi to Mathura ( quadrupling done but not commissioned). Mathura-Agra-Jhansi, third line sanctioned by CCEA in 2015, tenders called but nothing really happening under NCR one of the worst zones in IR. Jhansi-Bina, patch tripling taking place, Jhansi-Babina was to be commissioned by now, videos show tracks linked but no OHE. Bina-Bhopal-Habibganj took 8 years but finally triple lined, 120km. Bhopal-Itarsi started in 2015, only Bhopal-Bhadbhada track linking done(30km) and maybe commissioned this year. Bhadbhada-Budni(environmental clearance and difficult terrain in Satpuras has hampered the third line). Budni-Hoshangabad-Itarsi( yard work going on in Hoshangabad), new third bridge across Narmada complete in Dec 2018, should be commissioned soon. Itarsi-Nagpur, ghat sections, tunnels etc, a 18 km section in Teegaon-Chichonda ghat section to be commissioned March 2019 by Central Railway. The more serious engineering challenge is the viaducts and tunnels between Dharakoh and Ghoradongiri in this section of Nagpur-Itarsi. Doubling and attendant tunnel construction for the second line was done in 1966, Dad helped out in that, I assume the tunnels with 1966 emblazoned on them are still there(check it out while traveling on Tamil Nadu express, Karnataka express, rajdhanis or any of the Delhi-Hyderabad trains), he was a smart cookie. All you guys Shri A.R. Raichur, M. P. Pattani your work liveth for evermore, this young generation does not know what it was like to do tunneling projects in India in early 1960's, Ramganga hydel project, Giri Bata hydel project, Dandakaranya Bolangir Kiruburu railways, DBK railway, one of the best executed projects ever in India, came under budget and on time. I would not have been where I am without your shining examples of excellence in work.
Dad's light saber bought on June 12th 1947(it says so in the inside of the leather case in dad's neat hand-writing) is with me, you know those days all jedi knights carried a light sabre(their slide rule). The original single line was done in the late 1920's.
Nagpur-Wardha should be commissioned as quadruple tracks as it carries both east-West and North-South traffic, have been hearing of this 80km section for more than a decade, nothing. Wardha-Balharshah, only a 15 km section supposed to be commisoned after 3 years of work between Sonegaon-Chitoda.
Balharshah-Kazipet, only a 20km section near Mancherial triple lined and third bridge over Godavari commissioned last year. Many collieries and NTPC thermal plants here.
Kazipet-Vijayawada 214 km only a 10km section earthworks done and minor bridges done between Kazipet and Warangal: See for yourself. https://www.youtube.com/watch?v=ZPOP-7LdtE4&app=desktop
Between Vijayawada and Gudur earthworks have started in spurts here and there, Nellore, Ongole, Bitragunta, Kavali, etc. Take your pick, get happy, sad, https://www.youtube.com/watch?v=jM8o5rgH39Ihttps://www.youtube.com/watch?v=-xSPnU-3JTY
Between Gudur and Chennai-Central, quadrupling has taken place in some sections, Tiruvotiyur-Tondiarpet-MAS etc. catering mainly to Chennai suburban traffic that in the old, old days before 90% of the forum were born, me talk late 1950's went up to Gummidupoondi, now with a gazilion people in India all of India looks suburban. Now I think Chennai suburban may even go to Gudur. Don't know.