Atal Tunnel (also known as Rohtang Tunnel) is a highway tunnel built under the Rohtang Pass in the eastern Pir Panjal range of the Himalayas on the Leh-Manali Highway in Himachal Pradesh, India. At a length of 9.02 km, it is the longest tunnel above 10,000 feet (3,048 m) in the world and is named after former Prime Minister of India, Atal Bihari Vajpayee.

The tunnel reduces the travel time and overall distance between Manali and Keylong on the way to Leh. The route, which previously went through Gramphu, was 116 km (72.1 mi) long and took 5 to 6 hours in good conditions.

The traveller now reaches the South Portal of the tunnel from Manali, a distance of 24.4 km (15.2 mi) in about 50 minutes, goes through the 9.02 km (5.6 mi) long tunnel in about 15 minutes, and reaches Keylong which is 37 km (23.0 mi) away in about 60 minutes. 

The new route via the tunnel brings down the total distance travelled to 71 km (44.1 mi) which can be covered in about 2 hours and 5 minutes, a reduction of around 3 to 4 hours when compared to the earlier route.

Moreover, the tunnel bypasses most of the sites that were prone to road blockades, avalanches, and traffic snarls. The tunnel is at an elevation of 3,100 metres (10,171 ft) whereas the Rohtang Pass is at an elevation of 3,978 metres (13,051 ft). It was inaugurated by Prime Minister Narendra Modi on 3 October 2020. The cost of the entire project is ₹3,200 crore (US$438 million).

According to en.wikipedia