Salang Tunnel is hostile and toxic

Salang Tunnel is a high mountain tunnel at an elevation of 3.400m (11,154ft) above the sea level, located at the heart of the rugged Hindu Kush Mountain, a mountain range that stretches between central Afghanistan and northern Pakistan. It has insufficient lighting, inadequate ventilation and potholes.

The tunnel is 2.67-kilometre-long (1.66 mi) long and bypassed the challenging Salang Pass. It was built by the Soviet Union in 1964. It has become a traffic nightmare: it was built for a daily use of 1,000 to 2,000 vehicles and now between 7.000 and 10.000 vehicles pass through the tunnel daily. On a bad day, especially in the winter snow, hundreds of lorries form automotive centipedes that stretch 15km down the switchbacks at either end of the tunnel. If you do choose this route please check up to date information due to the security situation: terrorist attacks, ongoing armed conflict, risk of kidnapping and high crime rate.

Nestled between Parwan and Baghlan provinces, there’s a high danger of death from both crashes and carbon- monoxide poisoning. There is little by way of ventilation or illumination, and dust and fumes often reduce visibility to a couple of yards. It remains in use throughout the year.
It’s said to be one of the most dangerous tunnels in the world. This engineering marvel can be closed anytime due to deadly avalanches. When it was completed in 1964, it was the highest road tunnel in the world. The tunnel is located on the A-76 road and links Afghanistan's capital city of Kabul with the northern provinces. The surface of the road through the tunnel is now unpaved due the heavy traffic. The road to the tunnel is a mostly two-lane highway that winds through dangerous switchbacks high in mountains.
Pic: By Michal Vogt - [1], CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=7335181