4.4. Regression Analysis
shows the results of the general linear regression analysis for pedestrian collisions. Before undertaking the regression analysis in R, the multicollinearity between the explanatory variables was examined. Because the collinear variables could have the same information regarding injury severity in this study, and could lead to inaccurate estimates of coefficient values, collinearity needed to be avoided [59
]. Therefore, certain explanatory variables (such as commercial space ratio, green space ratio, single-family housing ratio, subway entrance density, and density of crosswalks without traffic signals), initially considered in this study, were excluded in the final analysis after preliminary testing.
The results of the analysis show that the explanatory power of the models for total pedestrian, incapacitation, and non-incapacitation injuries were higher than those for fatal and possible injuries. As Figure 1
shows, the analysis of total pedestrian injuries was similar to that for incapacitation and non-incapacitation injuries.
The effects of the indicators on pedestrian collisions were as follows: Population density, which was a proxy variable used to control exposure to pedestrian–vehicle collisions, was not statistically significant. The absence of an association between population density and pedestrian collisions in Seoul was not consistent with the significant influence found in prior research [11
]. This finding indicates that pedestrian accidents in Seoul were more likely to be affected by environmental factors than by the number of pedestrians. It may also imply that the occurrence and severity of accidents was more likely to occur among vulnerable road users [60
]. Therefore, in the future, it will be necessary for policies to take greater consideration of vulnerable road users, as well as improve the physical environment. However, this can also be seen as a limitation of the size of the spatial units, i.e., boroughs. The results may differ because of differences in the size of spatial units from other studies. Therefore, it is necessary to re-discuss the effects of population by analyzing them within a similar range of spatial units.
The proportion of residential areas shows a statistically positive relationship with total pedestrian, incapacitating, and non-incapacitating injuries. The results show that, the greater the number of residential areas, the more serious the injuries, coinciding with a previous study’s [38
] finding that fatal injuries tended to occur more in residential areas than in commercial areas. Accordingly, more deliberate attention should be paid to pedestrian safety in residential areas. High-rise multi-family housing, which accounted for the greatest percentage of residential areas in Seoul, failed to yield a statistically significant association with all types of injury severity. This result is within the same context as population density, with no statistical significance.
In addition, with respect to the proportion of housing in non-residential buildings (such as hotels, motels, or temporary dwellings), only total pedestrian and non-incapacitating injuries had a statistically significant influence. Therefore, the use of buildings may be more relevant to the likelihood of pedestrian injuries than their development density. This finding highlights that attention needs to be paid to neighborhood facilities at a micro-level, including parks, schools, children’s playgrounds, restaurants, and convenience stores [62
Among the road and traffic characteristics, it was found that the density of bus stops, which may indicate characteristics leading to walking, failed to have an explanatory power of association with injury severity, except in the incapacitating injury model. This result may indicate that pedestrian–vehicle collisions occurring around bus stops may result in more incapacitating injuries than other injury types. Therefore, more specific effective pedestrian safety policies should be considered for edestrian safety around bus stops, which support walking and sustainable transport uses. Regarding road types, only the secondary arterial road ratio showed a statistically significant association with injury severity (excluding fatal and possible injuries), suggesting that people may be more seriously injured on high-traffic roads than on neighborhood-level roads. This finding implies that vehicle speed on the road (which was not considered in this study because of limitations in the data acquired) may be associated with the severity of pedestrian crashes. This result is consistent with the previous literature [17
]. Therefore, policies and strategies are necessary for pedestrian safety on major roads where vehicle traffic is a priority.
The density of crosswalks with traffic signals was found to have statistical significance in all models, except for possible injury. In other words, pedestrian–vehicle collisions were more likely to result in serious injuries when such collisions occurred at crosswalks with traffic signals. This is likely to be caused by pedestrians crossing at a crosswalk when the pedestrian crossing light is red.
Therefore, pedestrians must be conscious of and comply with all signals to walk safely. In addition, from the driver’s point of view, installation of the pedestrian detection system in cars is suggested to reduce the possibility of collisions. Oikawa et al. [63
] asserted that the pedestrian detection system needs to be designed in manner to reduce the vehicle velocity at the moment of pedestrian contact. Interestingly, the number of crosswalks per road length was significantly correlated with injury severity, except for fatal injuries. Although these findings are consistent with prior research [20
], Kim et al. [5
] offered a contradictory finding, in that crossing at crosswalks was more likely to result in a lower risk of fatalities. This contradictory result may be confounded by other potentially influencing measures that were not considered in the study. However, the results of this study imply that pedestrian–vehicle crashes are likely to occur in neighborhoods with many crosswalks in general, beyond their relationship with the severity of accidents. Therefore, effective pedestrian safety programs, such as collision avoidance and pedestrian detection systems, are needed to reduce the likelihood of pedestrian crashes around crosswalks as well as the potential severity of pedestrian injuries. Xie et al. [27
] demonstrated the importance of exclusive pedestrian signals for all crosswalks, which can contribute to reducing the risk of pedestrian–vehicle collisions.
Finally, it is surprising that, among the factors with statistical significance, the density of speed humps was the only measure to have a negative influence on injury severity. Speed humps were likely to play a significant role in decreasing the injury severity [64
], even though the models of fatal and possible injuries did not yield statistically significant associations between pedestrian collisions and speed humps. As previously explained, in contrast to the tendency of secondary arterial road ratios to increase the likelihood of pedestrian crashes, collector and local roads did not show any association with the likelihood of crashes occurring. Therefore, policies that take advantage of the effectiveness of speed humps would be expected to play a role in reducing the possibility of pedestrian crashes on the collector and local roads.