Abstract Despite the advanced safety features in modern vehicles, accidents caused by unintended acceleration continue to occur, with “pedal misapplication” being a primary cause and a significant factor in serious accidents. The incidence of such errors is particularly high among elderly drivers. Autonomous emergency braking systems have limitations and cannot prevent all pedal misapplication accidents. Therefore, understanding the mechanisms behind these errors and developing effective preventive measures are crucial. Even elderly drivers without signs of dementia are prone to pedal misapplication, indicating that motor functions play a significant role. In this study, the control of lower limb joint mobility and muscle activity during pedal operation was analyzed, and specific indicators unique to elderly drivers were identified. The results revealed that the ability to adjust the speed and output of movement was insufficient in elderly drivers, and their capacity to suppress muscle activity declined. Reduced range of motion in the hip joints and diminished sensory function associated with aging may contribute to errors such as pressing both pedals simultaneously. Additionally, chronic conditions, including those caused by n eurological d iseases, a re r isk f actors a ssociated w ith p edal m isapplication. Even i n p atients w ith hemiplegic stroke, abnormal muscle activity was observed during pedal operation on the non-paralyzed side, potentially compromising the safety of such actions. Therefore, it is becoming increasingly evident that declines in motor control due to aging and neurological impairments are important factors associated with the occurrence of pedal misapplication accidents. Additionally, factors such as task focus during driving and dispersion of attention can affect pedal operation accuracy, with declines in both cognitive and motor functions being closely associated with these errors. Therefore, implementing comprehensive preventive measures that address not only cognitive functions but also motor functions is essential for preventing accidents involving elderly drivers.

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Head injuries of pedestrians and bicyclists in collisions with four-wheeled vehicles were analyzed using the Japan Traffic Accidents In-Depth Database, J-TAD (micro) which is maintained by Institute for Traffic Accident Research and Data Analysis (ITARDA). From the micro data, pedestrian and bicycle accidents in 2016~2018 were extracted. There were 116 pedestrian accidents and 60 bicycle accidents. We analyzed the relationship between the impacting part against the head and the impact speed in pedestrian accidents that resulted in brain injury. The results showed that the average impact speed exceeded 40 km/h in the case of windshield and pillar/hood collisions. In the case where the road surface was the impacting part, the impact speed was less than 30 km/h. This may be because collisions with a truck or a cab-over vehicle with a flat frontal profile pushed the pedestrian forward and caused collisions between the head and the road surface even at a relatively low speed. On the other hand, the average impact speed exceeded 40 km/h in the case of windshield, pillar/hood, and road surface in bicyclist accidents that resulted in brain injury. This is because there was only one pedestrian sustained a brain injury caused by contact with a cab-over vehicle and pushing down against a road surface. For both pedestrian and bicycle accidents, it was confirmed that brain injuries of AIS 3+ can occur even i n c ollisions w ith w indshields, w hich a re c onsidered t o h ave h igh p edestrian h ead p rotection performance when the impact speed is high. In the case of both pedestrians and bicyclists, various AIS 3+ injuries such as cerebral contusions, subdural hematomas, subarachnoid hemorrhages, and diffuse axonal injuries occurred in road surface collisions and windshield collisions. No relationship was found between the impacting part and the injury description.

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Motorcycle accident is one of traffic accidents types in Nagano Prefecture, where most of the population lives in hilly and mountainous areas. Motorcycle accidents, particularly single-vehicle accidents, are common in the prefecture, suggesting the influence of road alignment in causing the accidents. In this study, the authors analyzed the effect of road alignment on single motorcycle accidents in comparison with four-wheeled single-vehicle accidents, using statistical data on traffic accidents in Nagano Prefecture. The analysis covered 134 single motorcycle accidents (excluding mopeds) and 1,169 single four-wheeled vehicle accidents that occurred on general roads in Nagano Prefecture during the 11-year period from 2010 to 2020. The classification of road alignment was based on traffic accident statistics. The results showed that motorcycles were most frequently involved in accidents on downhill road alignments, accounting for approximately 40% (four-wheeled vehicles: approximately 27 %), and approximately 35 % (four-wheeled vehicles: approximately 16 %) of these accidents involved left/right curves, indicating that fatal and serious injury accidents were more common on downhill road alignments with curves. Furthermore, the fatal and serious injury accident rates for motorcycles were higher when the road alignment was a downhill left curve and an uphill right curve, at approximately 95 % (four-wheeled vehicles: approximately 55 %) and 91 % (four-wheeled vehicles: approximately 32 %), respectively. These results indicate that motorcycles are more susceptible to the effects of road alignments with gradients and left/right curves, and the unique road alignments such as downhill left curves and uphill right curves are particularly the contributing accident factors.

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Japan is one of the countries with a high rate of ageing. Although the number of traffic fatalities has been decreasing in recent years, the percentage of bicyclists killed in traffic accidents remains high, and prevention of accidents involving elderly bicyclists is important to reduce the number of traffic fatalities. Although several findings on driving behavior have been reported for bicyclists, there are few findings on roadway crossing behavior. We measured the driving behavior of 19 young and 15 elderly people while riding bicycles using a bicycle driving simulator that can safely simulate a dangerous traffic environment in a virtual environment realized by combining VR technology with a motion capture device. The subjects were tested on their "right-turn crossing ability," in which they crossed the roadside strip of a one-lane straight road while checking for safety, and on their "crossing route tracing ability," in which they traced the safe right-turn crossing route of the younger subjects, which had been measured in advance, as a model. The measured crossing behavior was analyzed, and the characteristics of the elderly were examined with a focus on the incidence of collision, lateral center of gravity sway, and the cube passing rate in the tracing inspection. The test results confirm that the incidence of collisions with older vehicles is higher than for younger people, particularly in the front lane. In addition, Analysis of the center-of-gravity sway during the straight-ahead driving period revealed that the center-of-gravity sway in the left and right directions was greater for the elderly than for the younger subjects. Furthermore, although the collision group of the elderly was significantly larger than the no-collision group in the right-turn crossing inspection, the trace inspection revealed that no significant difference occurred between the collision and no-collision groups. In addition, it was found that the cube passing rate of the elderly group by the trace inspection was significantly lower than that of the younger group. It was also found that the cube passing rate of the collision group was significantly lower than that of the non-collision group. The results suggest that the effect of aging on bicycle driving can be clarified from the cube acquisition rate and the lateral component of center of gravity sway, and that the increase in the lateral component of center of gravity sway during the straight-ahead period of bicycle driving, including rearward checking when crossing a right turn and steering ability can be used to estimate the factors causing accidents among the elderly.

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Recently, women who drove automobiles on a daily basis before pregnancy also continued to do drive after pregnancy. Approximately 3 % of pregnant women have experienced a motor vehicle collision during their pregnancy. Therefore, traffic safety education tailored to physical changes during pregnancy is an urgent issue. Hence, we conducted a longitudinal survey of the actual positional relationship between the abdomen and steering wheel while driving during the pregnancy period and targeted three pregnant women with no abnormalities during their pregnancy. The results showed that when seated in the driver's seat, pregnant women tended to increase the distance between the acromion and abdomen and decrease the distance between the steering wheel and abdomen according to their gestational week. A pregnant woman had a distance of less than 12 cm between the steering wheel and abdomen at seven months gestation. As the gestational weeks progressed, the protrusion of the abdomen made it more difficult for pregnant women to maneuver the steering wheel. This increased the risk of contact between the abdomen and steering wheel in a motor vehicle collision. Therefore, pregnant women should be provided with specific health guidance, such as observing the legal speed limit, maintaining sufficient distance between vehicles, and the correct way to wear a seat belt towards the end of their pregnancy. Furthermore, support should be provided to pregnant women to self-manage and assess whether or not they can drive a car themselves.

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