Evaluation of vehicle running performance on ash-covered roads.

The scale of volcanic eruptions influences the effects of wide-ranging disasters involving ashfall, such as the disruption of lifelines and paralysis of urban functions. This highlights the importance of vehicle availability on ash-covered roads for disaster management personnel involved in rescue and recovery efforts and for citizens who must evacuate or continue their social lives. We conducted tests to scientifically verify the running ability of vehicles on ash-covered roads. Results revealed that all-wheel-drive vehicles showed better running performance than two-wheel-drive vehicles, which get stuck when ashfall thickness exceeds 10 cm. Most of the vehicle's drive power is consumed as energy to scrape ash grains from under the tires, hindering sufficient propulsion. In addition, the tires sink into the ash layer, which increases driving resistance and causes the vehicle to get stuck. Running ability on ash-covered roads is mainly determined by the relation between the "drive system" of the vehicle and the "thickness of ash" on the roads. In addition, road surface conditions, including ash thickness, could change in time and space because of traffic volume and weather conditions.