Behavioral Modeling of Urban Freight Transport - Sustainable Urban Logistics: Concepts, Methods and Information Systems - page 224

policy effects. Our results allow us to comment on the distorted policy forecasts
that would be produced by simpler and rougher treatment of the information
acquired. On the base of recent evidence (Stathopoulos et al. 2011 ) we assume that
the relevant policy attributes for retailers are: (1) number of loading and unloading
bays (LUB); (2) probability of finding loading and unloading bays free (PLUBF);
(3) entrance fee (EF) charged to enter the LTZ.
The paper contributes to UGM literature by bridging a specific gap via in depth
investigation of retailers' preferences. Recent papers have investigated the role of
heterogeneity for both transport providers (Gatta and Marcucci 2013 ) and own-
account (Marcucci and Gatta 2013 ) agents with respect to policy intervention
whereas this paper focuses the attention on the presence and magnitude of non-
linear effects given the different levels of the attributes considered. Policy makers
usually intervene and evaluate policies assuming that attribute variations have
linear effects thus hypothesizing there is no dependence on the status quo (SQ)
level of the policy variable and, furthermore, that both increases and decreases
have symmetric effects on agent's utilities. The results reported show that one
cannot assume linear effects and consequently both the direction of the variation as
well as its magnitude should explicitly be considered when assessing a given
policy change. Having estimated the coefficients for the various attributes and
levels we calculate, via WTP measures, the biases that a linear assumption con-
cerning the effects implies.
The paper is structured as follows. Section 2 reports a short literature review
concerning agent-type analysis for UGM. Section 3 describes the survey instru-
ment developed and the data acquired while Sect. 4 reports and discusses the
econometric results and policy implications. Section 5 concludes and illustrates
future research endeavors.

2 Literature Review

Freight modeling is usually performed via aggregate models thus limiting the
attention dedicated to agent-level considerations that represent the appropriate
level of analysis to investigate if a behavioral approach to the phenomenon is
adopted. 2 This section succinctly summarizes recent literature that testifies the
increasing attention paid to behavioral issues in UGM. 3
Hensher and Figliozzi ( 2007 ) underline the weaknesses of the standard
approaches to UGM modelling. In fact, the modified four-step approach (M4SA)

2 UMG literature analysis also reveals a substantial heterogeneity in the approaches adopted
relates to the public or private perspective considered. The former mainly focuses on the
definition of policies for reducing the negative external effects on cities, while the latter
essentially aims at enhancing the efficiency of business operations (Corò and Marcucci 2001 ;
Marcucci and D'Agostino 2003 ).
3

For a definition of UGM see for example Ambrosini and Routhier ( 2004 ).