How will the US military exit Afghanistan? It may rely, at least in part, on a tunnel that's been called the "world's most treacherous," NBC News reports. A few people die each year from the carbon monoxide that persists in the 1.6-mile-long Salang Tunnel in the Hindu Kush mountains, and in 1982, a fire reportedly killed almost 1,000 Soviet troops in the tunnel. The Soviets built it in 1960s and it was, at the time, called "an engineering marvel," according to NBC. But the dangerously narrow tunnel been neglected for decades, leading to potholes so deep cars got stuck, thick exhaust that kept drivers from seeing much other than oncoming headlights, and poor ventilation. That's why the US has spent $19.5 million to improve it.
US troops haven't been able to use Pakistan's main border checkpoint for weeks, thanks to anti-American sentiment, so officials don't want to have to count on Pakistani routes when they pull out troops and equipment next year. By using the Salang Tunnel, they can go through Uzbekistan and Tajikistan instead. The US Army Corps of Engineers improved ventilation, paving, and lighting in the tunnel, but it's far from perfect, and will be much more expensive than the Pakistan route. As many as 28,000 vehicles and 40,000 shipping containers need to exit the country somehow, the Telegraph reported earlier this month. (Read more Afghanistan stories.)