Today, several costs caused by road traffic may either be only roughly approximated, or cannot be clearly assigned to the drivers causing them, or both. They are typically distributed evenly among a large fraction of drivers, which is both unfair and economically inefficient. We have built a prototypical platform, called the "Smart Tachograph", that allows us to measure traffic-related costs on an individual basis, thus supporting a more fine-granular charging of the responsible parties. Sensors observe the manner and circumstances in which a vehicle is driven, while several accounting authorities can evaluate this information and charge motorists on a pay-per-use basis. The Smart Tachograph offers valuable insights for the deployment of future ubiquitous computing services in general: its implementation has obvious requirements in terms of security and privacy; its deployment model is realistic through the strong economic incentives it offers; and its usage directly affects ...