5. Concluding remarks
This paper tests the non-linear effects of level variation for the attributes considered in a urban freight policy for the Limited Traffic Zone in Rome. The research focused on retailers’ and transport providers’ preferences eliciting them via a Stated Ranking Exercise. The results obtained indicate that, for the sample interviewed, nonlinear effects are more relevant for retailers with respect to transport providers. The bias introduced if non-linear effects are neglected increases with the distance the variation has with respect to the status quo. The paper contributes to the literature by underlining the potential impact of a phenomenon not usually considered relevant. The analysis is performed at an agent-specific level. Whereas in this case the non-linear effects alone are considered, previous research from the authors indicates that heterogeneity in preferences can be present also within single agent category. Future research will aim at: (1) increasing the number of respondents, (2) widening the type of policy instruments evaluated, (3) include other relevant stakeholders (i.e. citizens). Unfortunately, notwithstanding the detailed and cautionary suggestions provided, local decision makers in Rome have recently modified the regulatory framework by substantially increase the entrance fee in the Limited Traffic Zone without any compensatory measures. The decision taken does not bode well for the future. The upheaval it has provoked suggests that this policy intervention was considered as yet another form of additional taxation. This is not in line with the consultative approach adopted in other large cities with similar problems (e.g. Lindholm and Browne, 2013).
