Howrah–Prayagraj–Mumbai line

The Howrah–Prayagraj–Mumbai line, (formerly known as Howrah–Allahabad–Mumbai line) is a railway line connecting Kolkata and Mumbai via Prayagraj (formerly Allahabad). The 2160 km railway line was opened to traffic in 1870. This railway line was 2146 km until 2004. In 2004 the construction of Indira Sagar Dam submerged the old alignment near Khandwa & a new alignment of 14 km was relaid.

Sections
For more detailed study the cross-country line has been divided into smaller sections:
 * 1) Howrah–Bardhaman chord
 * 2) Grand Chord
 * 3) Bardhaman–Asansol section
 * 4) Asansol–Gaya section
 * 5) Gaya–Pandit Deen Dayal Upadhyaya Junction section
 * 6) Pandit Deen Dayal Upadhyaya Junction–Prayagraj section
 * 7) Prayagraj–Jabalpur section
 * 8) Jabalpur–Bhusaval section
 * 9) Bhusawal–Kalyan section
 * 10) Kalyan–Mumbai CST section

History
The first train in India traveled from Bombay to Thane on 16 April 1853. By May 1854, Great Indian Peninsula Railway's Bombay–Thane line was extended to Kalyan. It was extended to Khopoli via Palasdhari in 1855. Bhusawal station was set up in 1860 and Pune connected in 1863. In Eastern India, construction of the Howrah–Delhi main line was completed and through connection between Delhi and Kolkata was established in 1865. The last link was the bridge across the Yamuna at Prayagraj. In 1866 Bhusawal-Khandwa section was opened and GIPR also extended its operations to Nagpur. East Indian Railway, which had established the Howrah–Allahabad–Delhi line, opened the Allahabad–Jabalpur branch line in June 1867. GIPR connection over the Thull Ghat reached Jabalpur from Itarsi on 7 March 1870, linking up with EIR track there from Allahabad, and establishing connectivity between Mumbai and Kolkata.

The Bengal Nagpur Railway was formed in 1887 for the purpose of upgrading the Nagpur Chhattisgarh Railway and then extending it via Bilaspur to Asansol, in order to develop a shorter Howrah–Mumbai route than the one via Allahabad. The Bengal Nagpur Railway main line from Nagpur to Asansol, on the Howrah–Delhi main line, was opened for goods traffic on 1 February 1891. It was only after Kharagpur was linked from the west and the south that it was connected to Howrah in 1900.

The opening of this track was part of the inspiration for the French writer Jules Verne's book Around the World in Eighty Days. At the opening ceremony, the Viceroy Lord Mayo concluded that "it was thought desirable that, if possible, at the earliest possible moment, the whole country should be covered with a network of lines in a uniform system."

Electrification
In August 1976, the New Delhi–Howrah route (via Grand Chord), and that includes the Howrah–Allahabad section of the Howrah–Allahabad–Mumbai line, was the first trunk route in the country to be completely electrified with AC traction. Electrification of Itarsi - Jabalpur - Allahabad was proposed in Railway Budget of 2011. The entire route was divided into sections and electrification was completed in parts. In March 2020, electrification of last remaining stretch betweek Katni Jn. and Satna was also done, thereby the Howrah Allahabad Mumbai route became completely electrified.

Speed limits
Most of the Howrah–Gaya–Delhi line and Howrah–Bardhaman chord (the line is common with this line up to Allahabad) is classified as 'A' class line where trains can run up to 160 km/h but in certain sections speeds may be limited to 120 –. The line from Bhusawal to Mumbai is also classified as 'A' class. The Allahabad–Bhusawal sector is classified as 'B' class where trains can run up to 130 km/h.

Calcutta Mail
The Imperial Indian Mail (now called 12321 up /12322 down Howrah–Mumbai Mail via Jabalpur), running on this route, was possibly the first named train of Indian Railways. The Mumbai–Howrah Mail via Allahabad is called Calcutta Mail between Mumbai and Allahabad, and Mumbai Mail (some still call it by its old name, Bombay Mail) between Allahabad(Now Prayagraj) and Howrah. It is still running for 151 years as the oldest active train on this route covering 2160 km distance in 37 hours & 30 mins with an average running speed of 57.6 kph.

Inspiration for writing
The Kolkata–Mumbai linkage, along with other events, inspired the French writer Jules Verne to write his book Around the World in Eighty Days.