現在，緊急車両の緊急走行ルートは，出場指令を聞いた機関員が自作の地図をもとに,独自に決めている．しかし，地図の作成には 1ヶ月以上を要することがあり，機関員が管轄の地理状況を把握する必要性がある．また地図の作成方法や形式は，個々の機関員に依存している. 本研究では，これらの課題を解決するために，MMSによって取得した3次元点群を用いて，緊急車両が安全に活動できるかを判定するシステムについて検討する．
When a large earthquake occurs, it is presumed that there will be various property damages (e.g., bridge collapse, soil liquefaction, street cracks, building collapse, and utility pole collapse). Moreover, these property damages will obstruct emergency activities (e.g., firefighting activities and ambulance services), and cause the expansion of secondary damages. For securing the smooth and rapid emergency vehicles' activities, many local governments specify emergency transportation roads and are promoting the disaster mitigation strategies such as seismic retrofitting of roadside buildings. It is needed, however, to evaluate the effects of quake-resistant-conversion of roadside buildings on improving the accessibility of emergency vehicles quantitatively, because they are still unknown. In this paper, by evaluating the accessibility of emergency vehicles on specific emergency transportation roads (SETR) and the effects of quake-resistant-conversion of roadside buildings, the transportation function of SETR after a large earthquake is discussed as follows.
First, we construct a simulation model, which is consist of the following two sub-models. The one is the road blockage model that describes the collapse of each roadside building based on the Is-value (Seismic Index of Structure) of each building, and describes the road blockage based on the estimated effective width of each road in front of collapsed buildings. The other one is the emergency-vehicle-movement model that describes movement of emergency vehicles from neighboring prefectures to large scale rescue activity bases (LSRAB).
Next, performing the simulations, the accessibility of emergency vehicles using SETR in Tokyo Metropolitan Area is evaluated using accessibility indices. "Accessibility rate" is the percentage of LSRAB which can be accessed by emergency vehicles. "Increase rate of travel distance" is the ratio of the increment of the movement distance caused by the road blockage to the movement distance without road blockage. We examine the simulation results using these two indices for the following two cases.
Case 1 (the accessibility evaluation only using SETR): When emergency vehicles access LSRAB using highways /other roads of SETR under the current situation, the accessibility rate is 70.4 % / 27.3 % respectively. Moreover, the effects of seismic retrofitting of roadside buildings on accessibility is analyzed by assuming three scenarios. When the seismic retrofitting of 2.0% of roadside buildings in the order of lower seismic index of structure is achieved, the accessibility rate is improved from 70.4% to 92.6% / 27.3% to 64.0% respectively. This fact indicates that it is very important to promote seismic retrofit of buildings with lower seismic index of structure.
Case 2 (the accessibility evaluation using SETR and GETR): When emergency vehicles access LSRAB using SETR and GETR, the accessibility rate is 97.3 % under the current situation. Compared with case 1, the accessibility rate is significantly improved by 26.9 %. This fact indicates that GETR plays an important role in securing the function of SETR. Hence, it is important to conduct seismic diagnosis to roadside buildings located along GETR as well as SETR.
As it is predicted that there is a 70% possibility of an earthquake directly hitting Tokyo metropolitan within the next 30 years, it is an urgent issue to ensure the traffic function of emergency transportation roads (hereafter called "ETR"), which is an important infrastructure that supports emergency activities at the time of a large earthquake (e.g., wide-area evacuation, firefighting activities, ambulance services, etc.). In previous paper, we discussed about the transportation function of ETR after a large earthquake by evaluating the accessibility of ETR and the effects of quake-resistant-conversion of roadside buildings. In this paper, we propose the method for extracting vulnerable accessibility roadside areas, which have high possibility to hinder emergency activities after a large earthquake.
First, to extract the vulnerable roadside areas with poor accessibility, we propose novel indices, Link Isolation ratio (hereafter called "LI ratio") and Network Isolation ratio (hereafter called "NI ratio"). Next, we improve a simulation model, which we had previously constructed. This simulation model is consist of the following two sub-models. The one is the road blockage model that describes the collapse of each roadside building based on the construction year and the structure of each building, and describes the road blockage based on the collapse situation of roadside buildings. The other one is the emergency-vehicle-movement model that describes movement of emergency vehicles to activity bases. Then, performing the simulations, we evaluate the accessibility to disaster base hospitals (total 80 bases) using ETR in Tokyo metropolitan. We examine the simulation results with accessibility indices, LI ratio and NI ratio, which are calculated on the assumption that the medical relief activities are conducted at disaster base hospitals in the corresponding secondary healthcare service area.
LI ratio(pmin), the possibility of an emergency vehicle cannot access to any disaster base hospital, indicates higher value than road blockage ratio at 50.0% of road links, and there is a difference of 20.0 points or more between these indices at 15.5% of road links. This is because the isolation status of each road link is result of not only its own blockage status but also surrounding situations. From the spatial distribution of the LI ratio(pmin), we can grasp vulnerable roadside areas with poor accessibility to disaster base hospitals. For instance, it is difﬁcult to secure a detour route when emergency vehicle encounters road blockages in an area with sparse road network. In such areas, isolated links tend to occur over a wide range.
NI ratios(pmin) exceeds 50.0% at 7 disaster base hospitals (8.8% of the total). In the secondary healthcare service areas with those hospitals, there is a high possibility that the medical relief function is biased toward hospitals with high accessibility. Therefore, it is also important to consider the countermeasures to improve the accessibility to hospitals with poor accessibility. Moreover, NI ratios(pmin) indicate high value in secondary healthcare service areas such as Nishi-tama and Kita-tama Hokubu. At the time of a large earthquake, there is a possibility that some roadside areas become unreachable to any hospital and patients in those areas may not be able to receive medical relief activities. To improve NI ratios(pmin) of those areas, there is an urgent need to consider the countermeasures such as quake-resistant-conversion of buildings around disaster base hospitals or road links with high LI ratios.