Sensitivity analyses of the results

The required time to complete the evacuation for all strategies of evacuation (from maximum preventive up to minimum preventive evacuation) in the area of Zealand and the South Holland islands is presented in Table 20. Table 21 presents the relative difference with the reference situation for the same strategies for evacuation.

Table 20: Required time in hours to complete the evacuation for all strategies in the area of Zealand and the South Holland Islands

(1) Maximum preventive evacuation (2) High preventive evacuation (3) Low preventive evacuation (4) Minimum preventive evacuation

Max Min Max Min Max Min Max Min

Reference 24 53 21 38 21 38 16 18

Departure curve of 8 hours 23 52 20 37 19 36 9 16

100% follow up of instructions

29 66 24 43 24 42 16 16

1 person per car 45 >72 38 >72 38 >72 17 31

3 persons per car 20 40 18 30 18 29 16 16

Travel speed of 2 km/h 37 58 32 47 32 47 36 36 Travel speed of 40 km/h 24 53 21 37 21 37 15 17 Fallout of highway 44 65 38 64 38 64 18 23 Fallout of provincial (N) way 27 >72 24 61 24 60 16 28

Reduction outflow capacity 43 >72 36 71 36 70 17 30

Increase outflow capacity 18 37 17 27 17 27 16 16

Table 21: % change compared to the reference to complete the evacuation for all strategies in the area of Zealand and the South Holland Islands

(1) Maximum preventive evacuation (2) High preventive evacuation (3) Low preventive evacuation (4) Minimum preventive evacuation

Max Min Max Min Max Min Max Min

Departure curve of 8 hours -2% -2% -5% -4% -11% -5% -42% -42%

100% follow up of instructions 23% 24% 14% 14% 13% 13% 0% 0%

1 person per car 88% - 84% - 84% - 12% 77%

3 persons per car -14% -24% -14% -22% -14% -22% 0% -12%

Travel speed of 2 km/h 58% 16% 56% 25% 55% 26% 130% 130%

Travel speed of 40 km/h 0% -1% 0% -2% 0% -3% -4% -4%

Fallout of highway 87% 24% 84% 101% 82% 108% 14% 31%

Fallout of provincial (N) way 13% - 14% 92% 14% 93% 1% 60%

Reduction outflow capacity 79% - 71% 88% 71% 88% 11% 71%

Increase outflow capacity -25% -31% -18% -29% -19% -29% 0% -12%

When the best and worst performance of the scenarios in the sensitivity analyses are taken into account, a maximum bandwidth is shown in Figure 30. The difference between the maximum and minimum in the bandwidth increases when the number of people that preventatively evacuate increases; this was also expected because uncertainties in travelling are taken into account. It is shown that human choices can reduce the time required for evacuation, but it can also increase the required time for the evacuation of an area.

On average, the improvements in performance are less than the disimprovements in performance. This means that wrong choices, or human failure, can have a very large impact. Table 20 shows the time required to complete the evacuation (100% value) for each scenario in the sensitivity analyses. When the required time is more than 72 hours, it is presented as >72 hours because the lead time is less. Therefore, the results of the optimistic form of traffic management (max) and worst outcomes of both pessimistic forms of traffic management (min) are presented. The results show the parameters that strongly influence the performance of the evacuation.

Effort to reduce the window of time required for the departure curve from 16 to 8 hours is limited when a large number of people evacuate preventively. Only in the case of the minimum preventive evacuation will a reduction in the departure time significantly improve the total performance. Therefore, when congestion becomes more important, the departure curve becomes less important. When the population that evacuates increases (with 20% more compliance or when each car holds 1 person instead of the statistical average of 2, 19 persons per car) the time required for evacuation increases. An increase in compliance by 20% could result in an up to 25% increase of the required time for evacuation in this area in the case of a maximum preventive evacuation. Again, the congestion will increase. Strategies where the numbers of people that evacuate preventive are less because they evacuate vertical the increase in the required time will be less. When more people are in a car, the reduction in the required time is less than the situation when fewer people are in a car. Because of congestion, there does not seem to be a linear relationship. When the average travel speeds increase, the number of people per car matters the most when capacity of the road network is still available. The fallout of a highway means that only provincial N ways can be used. The consequences decrease when the road network is better used until the maximum capacity has been reached. The measures taken to support the outflow of an area also matters. Congestion, limited road capacity and accidents strongly influence the required time.

The results from other areas (see appendix E) show similar results, although some differences can be seen because of local characteristics, such as the size of the population and the road network and the capacity. For example, the fallout of a regional way has limited consequences in the area of Fryslan and Groningen because there are numerous possible routes.

The sensitivity analysis shows parameters with a high or low impact on effectiveness of evacuation. The impact of an increase of the travel capacity from 20 to 40 km/h and the impact of a smaller window of time for the departure curve (from 16 to 8 hours) have less than a 10% influence on the effectiveness of evacuation. Parameters with a high impact of more than 50% on the required time for evacuation are a reduction in the load per car (from 2.19 person per car to 1 person per car), a reduction of the average travel speed (from 20 km/h to 2 km/h), a reduction of the outflow capacity near the exists (from 0.2 to 0.1) and the fallout of roads when the number of roads is limited.

The parameters in the sensitivity analyses depends on the local characteristics, such as the number of inhabitants and vehicles used, the road network capacity and the possibility to adapt this traffic infrastructure for better use during an evacuation. The impact of the sensitivities increases when the number of movements increases – when more people evacuate preventively. Further improvements in the citizens’ response at the destination (for example the survival for these who shelter in place), although not taken into account in this research, can contribute to lower mortality rates. These become more important when other strategies besides preventive evacuation are chosen.

7.4

Impact of the citizens’ response on the effectiveness of