The challenge of including system effects and system boundaries into the environmental evaluation of road projects

The benefits of a road and the predominant part of the implications arise from the operation. The focus regarding the assessment of these various effects increasingly has to shift from the one-dimensional examination of road lines to the holistic view of infrastructure networks. The expansion of infrastructure and the expected benefits underlie a number of system effects. To begin with, feedback mechanisms exist, which are not taken adequately into account by the currently used (regional economic) models because of narrow spatial, temporal and causal system borders. Examples for that are countless: the omission of feedback mechanisms between infrastructure construction and mileage through the limitation on a single road section; the exclusion of intermodal alternatives or of the interactions between infrastructure and settlement structure. Beside these system effects, development trends increasingly show logistic functions which are caused by saturation tendencies. These trends can be found in system parts or the whole system (depending on the system borders) due to capacity limits, limited resources or endogenous limits like saturation tendencies concerning motorization, travel distances or the disposable household budget for transportation. These phenomena can be traced back to ecological and biological feedback loops. Therefore the choice of suitable criteria and indicators is crucial. Apart from the already addressed problems, it heavily depends on the chosen evaluation method. While the cost benefit analysis (CBA) focuses on the monetization of as many cost and benefit indicators as possible, the multi criteria analysis (MCA) depends on the choice of comprehensive key indicators. They must be able to describe sustainability and have to be cross-system, e.g. intermodal and including ecological, economical and social aspects. Furthermore, the key indicators should refer to development limits (distance-to-target indicators).