4 Typical Accident-Reducing Effect of Measures
  We analyzed the data to try to determine what types of measures were effective for what types of accidents. In the following, we discuss three types of measures selected from those implemented at the relatively large number of locations.
(1) Effect of installing road lighting and traffic directional markers at non-intersection locations
  The installation of road lighting and traffic directional markers is a means of reducing accidents by improving nighttime visibility. The graph in Figure 4 shows changes in the annual average number of nighttime accidents before and after measures, classified by type of accident, at 22 non-intersection locations where installation of road lighting or traffic directional markers was the only measure implemented.
  Accidents like head-on collisions and collisions with structures were significantly reduced, and it appears that driver awareness was enhanced because of improved visibility. The effect of these measures was to reduce the total number of accidents by approximately 35%.

Figure 4 Changes in Number of Nighttime Accidents, Classified by Type of Accident, at Locations Where Installation of Road Lighting or Traffic Directional Markers Was the Only Measure Implemented
(2)Effect of improving traffic light patterns at intersections
  This measure reduces traffic accidents by improving traffic light patterns so that traffic flows through intersections more suitably. We compared the average number of accidents before and after the measure, at 38 locations where traffic light pattern improvement was the only measure implemented (Figure 5).
  The total number of accidents dropped by approximately 17%; collisions while turning left showed a particularly high reduction, and accidents while crossing the road showed a tendency to drop. Although rear-end collisions remained at the same level, considering the fact that rear-end collisions on main arteries nationwide increased, the measure had an effect on this type of accident as well.The total number of accidents dropped by approximately 17%; collisions while turning left showed a particularly high reduction, and accidents while crossing the road showed a tendency to drop. Although rear-end collisions remained at the same level, considering the fact that rear-end collisions on main arteries nationwide increased, the measure had an effect on this type of accident as well.

Figure 5 Changes in Number of Accidents, Classified by Type of Accident, at Locations Where Improvement of Traffic Light Pattern Was the Only Measured Implemented
(3)Effect of installing right-turn lanes at intersections
  The purpose of this measure is to reduce accidents by facilitating the flow of traffic (especially traffic turning right) at intersections. Comparing the average number of accidents before and after the measure at 27 locations where installation of a right-turn lane was the only measure implemented, we found that accidents fell by approximately 38% overall and collisions while turning right showed a huge drop of approximately 48%. Because of the improved flow of traffic, moreover, rear-end collisions also showed a tendency to drop.

Figure 6 Changes in Number of Accidents, Classified by Type of Accident, at Locations Where Installation of Right-Turn Lane Was the Only Measure Implemented
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Institute for Traffic Accident Research and Data Analysis (ITARDA)