Transport within Afghanistan is rough, unreliable and sometimes dangerous. There is no rail network, road conditions vary wildly, and schedules are suggestions at best.
Domestic flights: Kam Air and Ariana Afghan Airlines operate limited domestic routes connecting Kabul with Herat, Mazar-i-Sharif and Kandahar. Flights cancel frequently. Book in person if possible and confirm repeatedly.
Shared taxis and minibuses: The most common way Afghans travel between cities. Shared Toyota Corollas and minibuses run on major routes -- Kabul to Jalalabad, Kabul to Mazar-i-Sharif via the Salang Pass, Kabul to Kandahar. Vehicles leave when full, not on a schedule. Journeys that look short on a map take many hours on mountain roads.
Roads: The Ring Road connecting Kabul, Kandahar, Herat and Mazar-i-Sharif is paved but poorly maintained in stretches. Secondary roads are often unpaved and impassable in winter or after rain. The Salang Pass (3,878m) connecting Kabul to the north closes regularly in winter.
Hiring a car and driver: This is the safest and most practical option for foreign travelers. Arrange through a local contact, guesthouse or travel agency. Do not attempt to drive yourself -- you need someone who knows the roads, the checkpoints and the local situation.
Security checkpoints: Taliban checkpoints are frequent on all major roads. Carry identification and any travel permissions at all times. Your driver or guide will handle most interactions, but be prepared for stops and questions.