Evacuation plan of Vesuvius Area: second level graph (urban roads). 

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... buses, shuttle buses in addition to scheduled public buses, temporary closing to the ordinary traffic of some roads, in order to create pedestrian, road and bus paths reserved to pilgrims. Also in this plan, like in the Vesuvius one, a suitable press campaign had to be carried out in order to adequately inform local residents to the changes of the circulation plan and of the public transport schedule, made to facilitate the flow of pilgrims through the city. The main difference between this campaign and the Vesuvius one is that it should be only an informative campaign thanks to joyful climate of the event, whereas the Vesuvius one should be an awareness campaign in order to avoid situations of panic. In 2008 garbage crisis has severely struck the city of Naples; for various months many tons of stinking, putrefying household waste lied uncollected along the streets of Naples district. The proposed dump in Chiaiano has become one of the most important strategic sites in Campania to face the emergency in the short run. Therefore the Italian Civil Protection Department commissioned to DITS a preliminary study on trash collecting and transport to the new Chiaiano dump. The aim of the study was to minimise the permanence of trash vehicles on the road network in order to reduce to the minimum their bad influences both on traffic congestion and on resident life quality (rank smells, waste percolate, etc.). Instead of the Vesuvius plan, in this case traffic flows of waste vehicles are in addiction to the normal traffic on road network as in the mobility plan of the 15th World Youth Day the pilgrims flow was in addiction to the ordinary one. In fact, in the Chiaiano case, normal activities continue despite the emergency state. Therefore, it is to note that also for the Chiaiano plan, as for the Vesuvius one, the boundary conditions, due to the emergency situation, have limited the possibility to identify alternative scenarios to be evaluated. In fact, it would be possible to close some roads to the ordinary vehicular traffic and reserve them only to the trash vehicles flow, if the particular socio-political conditions (large part of the population of the suburbs in the north of Naples was against the new dump and staged a long series of demonstrations often led into violence against police), which suggested to reduce to the minimum the impact of trash transport on resident population. About demand, for both Vesuvius and Chiaiano plans the traffic demand was well- known in advance and its quantitative assessment was not particularly difficult. It is to note that in both Vesuvius and Chiaiano cases Origin-Destination matrix was not to be estimated but it was determined or to be preliminary assigned. In fact, in the evacuation plan of Vesuvius Area the Origins and the extent of traffic flows depend on the number and dislocation of the residents in the zone of interest (the 18 towns of the “red zone”) and the Destinations were represented by the highway gates, which were preliminary assigned for each town to be evacuated on the basis of its intermediate destination (meeting point just outside the risk area) and final destination (reception centres in other Italian Regions). For Chiaiano plan there was only one Destination represented by the Dump and the Origins were towns and districts in the north of Naples identified by means of an uniform radial expansion around the dump, in which the constraint was represented by the dump maximum capacity of about 800 tons per day and the calculation of the waste production of each town and district has been made considering cautiously a pro capita waste production of 2 kg per day (see Table 1 and Figure 2). On the contrary, in the case of the World Youth Day additional demand due to pilgrims flow has been forecasted (see Table 2 and Figure 3).The Origins depended on the number of pilgrims coming in Rome and on the distribution of their accommodations in the Eternal City; so they had to be estimated. The Destinations were assigned and represented by the tourist bus parking areas and the meeting points for pilgrims near the celebration area of Tor Vergata. The definition of the graph (scheme of the transport network) was based in every three cases on the infrastructural characteristics of the existing roads network and transport system and was strongly influenced by the boundary conditions. About zoning, in the Vesuvius plan it has been carried out assuming as clusters the census sections of the eighteen town inside the “red zone”. Afterwards clusters have been aggregated around origin nodes, which were the access points of the road network identified for the evacuation. The adopted criterion for cluster aggregation has been to uniformly charge the road network, that is to move away the same number of persons from every origin node inside each town. The first level graph (highways and extra urban roads) and the second level graph (urban roads) are respectively shown in Figure 4 and Figure 5. In the case of the 15 World Youth Day zoning has been carried out by the identification and the following aggregations of the pilgrims groups accommodations in the city of Rome. Afterwards for each origin node a multimodal path to the event location has been defined. In the Chiaiano plan the graph was formed by three main paths to the only Destination represented by the dump, which were connected to the rest of the road network selected for the trash transport by means of a road ring identified around the dump (see Figure 6). Inside each town and district in the north of Naples as origin nodes the trash vehicle depots and as destination nodes the road intersections between of the above mentioned ring with the whole road network interested by the trash transport. In the Vesuvius plan the demand assignment is entirely deterministic. In fact, during the transferring phase, the ordinary traffic is almost equal to zero and the whole road network is orderly used almost exclusively by the population to be evacuated, under the police control. In these exceptional conditions it was not possible to establish resident behaviour because of the lack of historical data; therefore it was no possible to make the traffic assignment by means of standard speed-flow diagrams. The routes with the highest capacity have been chosen because of the necessity to evacuate the greater number of people in a very short time. Although the assignment was deterministic, the application of plan presents some random elements due to the behaviour of the population which, in a panic situation, could not follow the scheduled routes. In the case of the 15 th World Youth Day to the stochastic assignment of the ordinary flow is added the oriented but anyway stochastic surplus due to the pilgrims flow. The traffic assignment has been made by means of standard speed-flow diagrams. For each origin node a multimodal path to the event location has been defined (see Figure 7). The choice of routes is not imposed, but it is let to pilgrims, on the basis of the generalized travel cost, among a number of recommended paths which have been planned by the organizing committee. The plan hypothesizes the use of additional shuttle buses to satisfy part of the transport demand. In this study it is very significant the control and management of the public transport system too. In the Chiaiano plan to the stochastic assignment of the ordinary flow is added the deterministic surplus due to the trash vehicles flow. The traffic assignment has been made by means of standard speed-flow diagrams. For the routes assignment three type of criteria have been considered: minimum urban impact route, minimum travel time route, minimum travel length route and, finally, because of the particular political-social conditions and of the necessity to minimize the impact of trash transport on resident population, the route with the minimum urban impact has been chosen. As an example the flow assignment made on the basis of minimum urban impact criterion is shown in Figure 8. In Vesuvius evacuation plan a suitable informative campaign assumes a role of great importance to prepare local residents to the event and therefore to avoid situations of panic. Also in the World Youth Day plan a suitable press campaign had to be carried out in order to inform local residents to the changes of the circulation plan and of the public transport schedule, made to facilitate the flow of pilgrims through the city. The main difference between this campaign and the Vesuvius one is that it should be only an informative campaign thanks to joyful atmosphere of the event, whereas the Vesuvius one should be an awareness campaign in order to avoid situations of panic. Finally, in the Chiaiano plan the atmosphere of general strong disapproval suggested to pass the waste transport to the new dump over in silence; therefore an information campaign was not carried out because it would be counter-productive. The analysis of the various phases of the three examined cases shows that the characteristics of the plan are strongly influenced by the boundary conditions due to the particular kind of exceptional event, which determines the different plan goals: In fact, in the case of the evacuation plan of Vesuvius Area the objective is to minimize the total time of evacuation and, therefore, to maximize the outflow of residents (people per hours); in the case of the 15 th World Youth Day the aim of the study is to satisfy the surplus of transport demand avoiding the collapse of the urban transport system; while in the study of trash transport to the new Chiaiano dump the goal is to minimize the permanence of trash vehicles on the road network in order to reduce the impact on traffic congestion and on resident life. As an example, it is plain that in the Vesuvius case the availability of more time for the evacuation or of a more capable road network, in terms of roads width or numerousness, could lead to ...