## 5 Conclusions  
During a disastrous seismic event, the debris of buildings interfering with the road network is the main cause of urban mobility disruption. Nevertheless, the literature that develops fragility curves for infrastructures subject to seismic actions focuses upon geotechnical effects, and does not provide fragility curves based on this important type of road blockage.  
For a generic road network segment in an urban area, a fragility curve constructed with the proposed framework can interpret the debris distribution phenomenon of the damaged buildings. More specifically, for a given seismic intensity measure level, the developed fragility curves express the probability that the road is open or closed to the transit of emergency vehicles after the debris fall. The proposed procedure is specifically tailored for the minimum set of information provided by the LCE  
Figure 13: Comparison of the results with the real case (PGA = 0.87 g) for (**a**) AC1 and (**b**) AC2.  
analysis, and is based on the construction of debris graphs and the use of the maximum likelihood estimation method.  
If in a road network segment there are also other causes of mobility disruption related, for example, to the damage to bridges, retaining walls, etc., the relevant fragility curves can be assumed to work in series. This implies that the probability of opening (or closure) of the generic road segment is based on the product among the probabilities of opening (or closure) of the various fragility curves interpreting the different phenomena.  
In this work, the fragility curves were developed for the portions of road having the highest risk for loss of connectivity (critical areas), but they can be defined by applying the proposed methodology to all portions of a road between two opposite structural aggregates. Additionally, in this case, the fragility curves of the different portions can be assumed to work in series. Such aspects can be valuable for future research. In the current opinion of the authors, it is sufficient to focus on the critical areas of the road network segments, thus avoiding laborious data analysis. In these areas, defining the debris widths according to the geometric characteristics of the entire structural aggregates, the interactions among the debris heaps of the different buildings constituting the aggregates and the relative distribution of the blockages along them can be sufficiently taken into account.  
Conceptualization, A.A.; methodology, A.A.; validation, A.A., F.M. and M.V.; formal analysis, A.A.; investigation, A.A., F.M. and M.V.; data curation, A.A.; writing--original draft preparation, A.A., F.M., M.V.; writing--review and editing, A.A., F.M., M.V.; visualization, A.A.; supervision, F.M. and M.V. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
This research was supported by the Italian Civil Protection Department within the project \"Contratto concerne l'affidamento della Governance in materia di riduzione del rischio ssimico e vulcanico ai fini di protezione civile nell'ambito del PON Governance e Capacita Istituzionale 2014-2020--CIG6980737E65\". Authors would like to thank [PERSON] of the Italian National Research Council--IGAG, and [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] of the Italian Civil Protection Department for the useful discussions.  
The authors declare no conflict of interest.