This is the road from Peshawar to Kabul in Afghanistan, is one of the highlights of this region. This legendary Pass has played an important role on the trading roads from India via Pakistan to Afghanistan and Persia.
You need a permit to access this Pass. When you go for the permit, some heavily armed soldiers of the Frontier Force will also accompany you.
The reason they join you is security. Don't forget this is Tribal Area. In this area there was (and still is) a lot of smuggling (drugs, weapons,...) and these actions aren't without risk and danger.
The Khyber Pass railway goes through 30 tunnels and crosses 92 bridges but nowadays it can be used only for a small part because the rails are gone due to landslides.