Study on the Relations between Drivers' Behavior and Road Alignments and Visual Environment at Sag Sections on Expressways.

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In this study, we concern the relations between drivers' behavior and road alignments and visual environment at sag sections on expressways. The major point of this study are as following :(1) Important results of chapter-2 are as follows. 1) It was quantitatively clarified that three factors influenced characteristics of the acceleration between the starting at signalized intersection and the stable following driving. Factors analyzed here, are the attributes of drivers, time headway at the signalized intersection the vehicle started, and the stable speed of leading vehicle. It was also clarified that the effect of drivers' age is significant. 2) The effect of the drivers' attributes had common effects to different road sections. It was confirmed that acceleration of aged drivers is lower than the others at flat or incline section, and is more than the others at decline section. These observations were confirmed at simple incline and decline section as well as sag section. 3) At sag s … More ection, driving pattern that relatively big deceleration was generated in sag bottom and upgrade interval because the headway became small at decline section. The relationship between such deceleration pattern and acceleration of flat area was not observed. This means that even aged drivers with gentle accelerating at flat area may have risk of such sudden decelerating.(2) The data of drivers' behavior at sag section were collected with driving simulator. And in order to make clear the decision-making process of drivers' behavior, the present study used "protocol analysis". The main result of protocol analysis is that the grounds to exclude the data were obtained and it was found out that rousing drivers to recognize the change of inclination is important. Analysis results of the data of drivers' behavior revealed the effectiveness of the alternative proposed for improvement of radius of vertical curves and frontal visibility(3) The repetition experiment by one subject using the Simulator produces platoon traffic stream made of only one particular driving behavior parameter. Those streams are produced for ten subjects, and it is found that such uniform stream still form a kind of shock wave phenomena. On the other hand, another type of experiment, which produces platoon traffic streams made by several subject on seven types of road vertical alignment, is carried out. The condition of vertical alignments is different in algebraic difference of upstream and down stream grade at a sag section ('algebraic grade difference') and in 'vertical curve length'. The experiment shows that not most steep grade change of sag sections produces deceleration shock wave and also most gentle grade change does it. Some particular characteristics of a subject of traffic stream might cause deceleration shock wave. Less