交通プロジェク卜の便益の定義について

弱等価的偏差(WEV)の提唱

抄録

The aim of this paper is to propose a new definition of social net benefits, called the weakly equivalent variation (WEV) in this paper, which is defined as the minimum amount of compensation that the society needs in order to give up a proposed transport project while remaining at the after-improvement welfare position.
Although it has been recently advocated that the best index for measuring social net benefits is the so-called socially aggregated equivalent variation (ΣEV), this paper shows that our WEV is a better definition than ΣEV in the following two points: First, as well as ΣEV, the positivety of WEV is a sufficient condition for passing the Kaldor -Hicksian compensation test whenever the latter is meaningful. Second, Unlike ΣEV, WEV can be measured by a short-cut method to evaluate the overall impacts of transport project by analysing only the direct output of the project, i.e. transport market.
The difference between our WEV and ΣEV lies in the treatment of prices other than the transport cost. For ΣEV case, these prices are exogenously fixed at the prechange level. For our WEV case, on the other hand, these prices are indogenously determined within the framework of the compensated equilibrium, which is invented in order to obtain the minimum amount of compensation that the society needs in order to give up that transport project while every household in the soceity remains at the post-improvement welfare position.
By using the compensated market clearance conditions, for our WEV case, the incidence form of WEV can be transformed into its origin form, where the incidence form is an expression of WEV in terms of the consumer's good demand and factor supply functions, and lump sum income composed of the profit share endowment and tax burden. And the origin form is that in terms of the consumer's and producer's transport demand functions only, which makes us to have a shortcut measurement of WEV. For ΣEV case, on the other hand, because all prices are fixed at the preimprovement level, it cannot be transformed into its origin form.
Finally, because even our origin form of WEV needs the compensated transport demand functions and compensated equilibrium prices, through the Taylor's expansion, this paper proposes an approximation measurement method which uses only the Marshallian transport demand functions and post-improvement equilibrium prices.