While the south portal of the tunnel is near Manali, standing at a height of 9840 ft, the north portal is at Sissu in the Lahaul valley, at a height of 10,171 ft. Prior to the construction of the tunnel, the highway remained closed during winter season for six months, isolating Lahaul and Spiti from the mainland. The Atal tunnel not only opened all-weather travel, but has also reduced the distance on Manali – Sarchu road by 46 kms and travel time by four to five hours. A journey from Manali to Lahaul and Spiti Valley that once required more than four hours now takes just 15 minutes. Moreover, the tunnel bypasses most of the sites that were prone to road blockades, avalanches, and traffic snarls.

Built by BRO and as a joint venture of Shapoorji Pallonji Group-run Afcons and Strabag of Austria, the horseshoe-shaped, single tube double lane Atal tunnel has a roadway of 8 metres. It has an overhead clearance of 5.525 metres. Also, it is 10.5-metre wide and has a 3.6 x 2.25 metres fire-proof emergency egress tunnel built into the main tunnel itself. There are 18 egress tunnels where after every 500 metres there is an opening in case of emergency. The tunnel has ample safety features built into it including telephone connections at every 150 metres for emergency communication, fire hydrant mechanisms at every 60 Metres, auto incident detection system with CCTV cameras at every 250 metres, air quality monitoring at every one kms, evacuation lighting/exit signs and broadcasting system throughout the tunnel among others. The Atal tunnel has been designed for traffic density of 3000 cars and 1,500 trucks per day with max speed of 80 km/hr. It has the state-of-the-art electromechanical system including semi transverse ventilation system, where large fans separately circulate air throughout the tunnel. The tunnel also has a public announcement system to make important announcements in emergency situations for which loudspeakers are installed at regular intervals. The tunnel is also the world’s first tunnel that offers 4G internet connectivity. Atal tunnel was built with 14,508 metric tonnes of steel and 2,37,596 metric tonnes of cement. Around 14 lakh cubic metres of soil and rocks were excavated using the drill and blast technique for excavation. It was constructed using drill and blast NATM (New Austria Tunnelling Method) techniques. Afcons deployed 1,000 workmen and 150 engineers for the project.

The historic decision to construct a strategic tunnel below the Rohtang Pass was taken on 3 June 2000 by Atal Bihari Vajpayee and the foundation stone for the access road to the south portal of the tunnel was laid on 6 May 2002. However, after a change in the government at the centre, the project came to be neglected for many years, with only 1.3 kms completed by 2014. When Prime Minister Narendra Modi took office that same year, he resurrected and fast-tracked the project. In 2005, the estimated cost of this tunnel was projected at ₹950 crore, but due to continuous delay, the tunnel was finally completed after spending over ₹3,200 crore.

The Atal tunnel has officially been certified by World Book of Records, as the ‘World’s Longest Highway Tunnel above 10,000 ft. The tunnel, besides offering the Armed Forces a strategic advantage by providing an alternate link to the critical Ladakh Sector, has also been a boon for the residents of Lahaul and Spiti district in Himachal Pradesh. The region has seen an unprecedented increase in the arrival of tourists, and the valley and the state have witnessed growth in their socio-economic domains. Eight thousand houses of the Lahaul valley of Himachal, who would otherwise spend their winter season in darkness, got electricity as the valley’s power grids are now being fed through a 33 kV transmission line laid across the Atal tunnel. Besides supporting the Armed Forces, the Atal Tunnel is destined to play a defining role in the future development of the region.