Writing in Viewpoint: Measuring success in Afghanistan, Fotini Christia, a political scientist at the Massachusetts Institute of Technology who has recently spent time in Afghanistan researching conflict and development says:

The cost of transporting goods is increased by violence and the chances of being attacked on the roads. If transport costs on a route were to fall it would be a positive sign.

In 2007 Afghanistan’s lorry drivers’ union estimated that each vehicle pays more than $6,500 (£4,216) annually in taxes and bribes extorted on Afghanistan’s roads.

Such costs are an important measure of the security situation.