Which bridge is the longest rail-cum-road bridge in India ?

Bogibeel bridge is a combined road and rail bridge over the Brahmaputra River in the northeastern Indian state of Assam between Dhemaji district and Dibrugarh district, which was started in the year 2002 and took a total of 200 months to complete, Bogibeel river bridge is the longest rail-cum-road bridge in India, measuring 4.94 kilometres over the Brahmaputra river. As it is situated in an earthquake-prone area it is India's first bridge to have fully welded steel-concrete support beams that can withstand earthquakes of magnitudes up to 7 on the Richter Scale. It is Asia’s 2nd longest rail-cum-road bridge and has a serviceable period of around 120 years. It is the 5th longest bridge in India after Bhupen Hazarika Setu, Dibang River Bridge, Mahatma Gandhi Setu and Bandra-Worli Sea Link. The bridge was constructed by a consortium of construction companies headed by Hindustan Construction Company. The bridge has a double rail line on the lower deck and a 3 lane road on the upper deck.

It was inaugurated by prime minister Narendra Modi on 25th December 2018 on the occasion of Good Governance Day.

The Bogibeel bridge traces its origins to the Assam Accord of 1985 and was one of several major infrastructural projects to be set up in Assam in accordance with the pact. It was sanctioned by the Government of India in 1997-98 and was expected to be completed by the end of the Ninth Five Year Plan. The foundation of the bridge was laid in January 1997 by Prime Minister H.D.Deva Gowda, but its construction was inaugurated only in 2002 by Prime Minister, A.B. Vajpayee.The project was to be completed in six years following the inauguration, however the work did not begin until 2007, owing to lack of funds and attention. Consequently, that same year, the Bogibeel bridge was granted a national project status by the Government of India in 2007 by Prime Minister Manmohan Singh, but the implementation was slow, notwithstanding a Congress government in Assam. Accordingly, the Union Ministry of Finance funded 75% of the project costs while the Ministry of Railways financed the rest. The actual work on the project only began in 2011.

In April 2008, the Northeast Frontier Railway contracted Gammon India to construct the sub-structure of the bridge while a consortium of Hindustan Construction Company, DSD Brückenbau GmbH, Germany and VNR Infrastructures won the bid to build the superstructure.

The bridge witnessed huge time and cost overruns over time. The cost, initially estimated at ₹1,767 crore (US$250 million), escalated to ₹4,996 crore (US$700 million) by 2014. According to a press release by the Indian Ministry of Railway on 25 July 2014, in the main bridge, 36 out of 42 well foundations and 28 out of 40 piers had been completed, while 2 out of 41 girders had been launched. An expenditure of ₹3,041 crore (US$430 million) was incurred on the project till March 2014, and a further outlay of ₹600 crore (US$84 million) was sanctioned for the year 2014-2015. The project was now expected to be completed by March 2017. However, a correspondent writing in The Hindu Business Line revealed that when he visited the project in July 2014, only 15 out of the 42 piers were "coming up", while the work on the rest had "barely" begun.

On 2 December 2018, the bridge opened as the first freight train crossed it. On 25 December, the Indian Prime Minister Narendra Modi inaugurated the Bogibeel bridge, on the birth anniversary of former Prime Minister Atal Bihari Vajpayee, and also flag off an intercity express connecting Tinsukia and Naharlagun. The overall cost of the project ultimately escalated to ₹5,960 crore (US$840 million). The total length of the bridge also increased from 4.31 kilometres (2.68 mi) to 4.94 kilometres (3.07 mi).