The Pamir highway leads from the city of Osh, Kyrgyztan, through Tajikistan (Gorno-Badakhshan Autonomous Province, Khorugh, Dushanbe), via the eastern part of Uzbekistan, to Mazari Sharif in northern Afghanistan.
Most of the Pamir Highway is paved, exept for the mountain passes. Secondary roads are mostly unpaved and in very bad condition. The Pamir highway is mostly one laned. The pavement condition depends, sometimes it is really bad. Mistakes in driving can have deadly consequences, because the road is small and leads trough deep valleys. Crash barriers doesn't exist.
On the Pamir Highway seems to be almost no traffic, but for that reason nearly everybody stops. A small payment can be expected, make it clear before you enter. Russian language is common. You need special permits for some regions along the Pamir highway, which must be cleared before you enter. Call your responsable embassy for that reason. Be aware of the landmines down in the Panj River.