NON LINEAR EFFECTS OF URBAN FREIGHT TRANSPORT POLICIES: A RETAILER'S PERSPECTIVE.

Decision makers in urban freight transport (UFT) typically need to assess the impact new policy interventions might have on freight distribution. They need to assess the impacts of changes in freight distribution policies might have on a set of elements among which one can safely include: infrastructure needs and use, logistic performance, emissions and energy use. All these elements can be grouped and summarized in two macro-objectives; in fact, policy intervention objectives usually include the minimization of negative economic effects and the reduction of the environmental impact freight distribution provokes. The effects of policy changes are inextricably related with the extant regulatory framework that also influence the relationships among the various actors interacting along the supply chain. The operators commonly considered important, given the crucial role they play in UFT, are: retailers, transport providers, and own-account. Notwithstanding the admittedly important role that a detailed knowledge of these three agent categories have for a correct policy implementation there is a limited knowledge concerning the specific preferences and behavior of each agent-type. It is de facto assumed that retailers, own-account and transport providers have homogenous preferences and can be seamlessly treated. The upsurge of behavioral models and the acquisition of data necessary to predict goods and vehicle flows both under the current and, more importantly, under altered policy/regulatory conditions explains the progressive importance that is attributed to an agent-based perspective. This research reports the result of a stated ranking exercise (SRE) conducted in the Limited Traffic Zone (LTZ) in 2009 in the city center of Rome focusing on retailers which demand freight transport services and play an important role in extended supply chains. The lack of knowledge under this respect is most notably due to the difficulty and cost implied in acquiring the necessary data for estimation purposes. This paper proposes a comparison between two different MNL specifications where non-linear effects for the variations of the levels of the attributes considered are studied and detected. A meaningful comparison between willingness to pay (WTP) measures derived by the two model specifications is proposed so to avoid known scale problems. The results obtained are very interesting and meaningful from a policy perspective since they show potentially differentiated effects of the policy implemented in deep contrast with the, often assumed, homogenous effect hypothesis.