Engineers confirmed that the tunnel will be operational by May-June 2020.
A frequent visitor to this picturesque resort before illness gripped him, late Prime Minister Atal Bihari Vajpayee is believed to be the only national leader who thought of ending the five months of exile every year of the residents of the landlocked Lahaul Valley by constructing a tunnel through the Rohtang Pass.
Locals believe Mr Vajpayee was the man behind cementing the "tunnel of friendship" being drilled at 3,000 metres above sea level beneath the Rohtang Pass. In all probability, the tunnel will be operational by May-June 2020, engineers said.
"The construction of the tunnel is about the promise that Vajpayee-ji made to Tashi Dawa before his old friend died in December 2007," Mr Dawa's son Ramdev told IANS on the phone.
The strategically important tunnel will ensure all-weather connectivity to Lahaul-Spiti district that otherwise remains cut off from the rest of the country for more than five months owing to the closure of the Rohtang Pass (13,050 feet) due to heavy snowfall.
Tashi Dawa alias Arjun Ram Gopal, a resident of Tholang in Lahaul-Spiti, was credited with convincing Ayalji to take up the tunnel construction that will bring economic prosperity in the otherwise snow-bound, inhospitable region.
"It would be a historic day for all the people of the Lahaul Valley when the tunnel is completed," an emotional Ramdev, a government employee, who is retiring this year, said.
Ramdev said Mr Vajpayee and Dawa became friends during a training camp organised by the Rashtriya Swayamsevak Sangh (RSS) at Baroda (now Vadodara) in the then Bombay Presidency in 1942.
Septuagenarian Mehar Thakur, who is now settled here, said: They (Vajpayee and Dawa) were thick friends. Whenever Atalji used to visit Prini he used to call Tashi. They used to share their nostalgic moments for hours."
Prini is located on the outskirts of this tourist resort. Mr Vajpayee last visited the house, currently out of bounds for people, for a quiet sojourn in June 2006. That was two years after his government was voted out in the national elections. Since then the house wears a deserted look. Neighbours fondly recall the days when Mr Vajpayee as Prime Minister came here every summer and mingled with the locals.
Atal Bihari Vajpayee, as Prime Minister, had announced at a public meeting in Keylong, the district headquarters of Lahaul-Spiti, in 2002 that a tunnel would be constructed beneath the Rohtang Pass. Solang, popular among skiers for snow and steep pistes, or ski tracks, just 13 km uphill from Manali, still has a foundation stone of the Rohtang tunnel.
The stone reads: "Commissioning of works for access road to south portal of proposed Rohtang Tunnel by Prime Minister Shri Atal Bihari Vajpayee."
"Development and defence, for both aspects this Rohtang tunnel was much required and today it is going to be started," Mr Vajpayee had announced at a public meeting in Manali on May 24, 2002, where then Chief Minister Prem Kumar Dhumal was also present.
Remembering one of his visits to Atalji's house, former village head Kundan Lal said he was once honoured by the former Prime Minister with a cash incentive.
"I presented a wall clock to Vajpayee-ji which was made by me from junked motorcycles. He was so delighted to receive it that and he gave me a cash reward of Rs 1,000 to support my initiative," Lal, who was earlier running a motor workshop in Prini, told IANS.
Locals also remember Mr Vajpayee as an environment protector.
Prini village head Shiv Dayal said Atal Bihari Vajpayee used to say plant two-three saplings rather than planting 100s as it was easy nourish them adequately.
Mr Dayal said the Rohtang tunnel should be named after Mr Vajpayee and this would be a befitting tribute to the great leader.
Mrs India 2017 winner Kalpana Thakur, who runs a hotel in Prini, fondly remembered one of her interactions with Mr Vajpayee in 2003.
"Vajpayee-ji asked me the name of my son and he explained me my son's name (Srijan) in his poetic style," she recalled.
Besides as an orator, poet and statesman, locals remember Mr Vajpayee's love for trout fish on a platter during his stay in Prini.
During his 2001 visit, Atal Bihari Vajpayee told reporters that he composed his poem "Unchai" at Prini.
The most ambitious and expensive undertaking of its kind, the excavation of the 8.8-km long horseshoe-shaped tunnel under the Rohtang Pass in the Himalayas was completed last October. Only some civil engineering work is pending, officials said.
Later, the tunnel's foundation stone was laid by United Progressive Alliance (UPA) chairperson Sonia Gandhi on June 28, 2010, in the Solang Valley.