The tunnel is of questionable safety but strategically important
The Salang Tunnel is the only major north-south route in Afghanistan to remain open throughout the year.
Providing the shortest all-weather route, the tunnel and the road through it cut the alternative journey from Kabul to the north by 300km (186 miles), bypassing Bamiyan in central Afghanistan.
Crossing the Hindu Kush mountain range under the treacherous Salang Pass, the 2.6km (1.6 mile) tunnel bisects north-east Afghanistan, reaching an altitude of about 3,400m (11,154ft) - making it one of the highest road tunnels in the world and only slightly lower and shorter than the Eisenhower Memorial Tunnel in the Rocky Mountains of the US.
Plans for its construction - with help from the Soviet Union - were put forward in the mid-1950s.
And it was hailed as an engineering masterpiece on completion in 1964.
On a typical day, about 1,000 vehicles pass through the tunnel, but there is nobody controlling the traffic apart from the under-staffed and under-resourced Kabul-Salang highway department.
And critics say it has insufficient lighting, inadequate ventilation and potholes.
It was badly damaged by fire in 1982 and partially destroyed in the late 1990s by mujahideen led by Ahmad Shah Masood fleeing the Taliban's advance from Kabul.
At the time of its re-opening in 2002, the Halo Trust - a charity that provided machinery and manpower to blast away masonry and debris - called the tunnel "a tragedy just waiting to happen".
And some say the authorities were irresponsible to allow vehicles to travel in the tunnel and its surrounding area with a high risk of avalanches.