Roads
Afghanistan just has one major transit road which connects Herat, Kandahar, Ghazni, Kabul and Kunduz.
The road before Herat is good, Kunduz to Shir Khan Bandar is good too. Everywhere else, expect the roads to be downright terrible.
Traffic rules
There are no traffic rules (oh yeah, don’ drink and drive) and hence, no traffic police. Most cars do not have a license plate. There is no import tax or form to fill in when entering the country with your car or motorbike.
Petrol
It is about 0.85-1 dollar per litre for octane 95. Petrol stations are widely available.