特定緊急輸送道路のアクセシビリティ評価と沿道建築物耐震化の効果

抄録

 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.