Studies on evaluation of geometrical design of forest roads by driver's psychological and physiological response: Alignment description of forest roads with variation in systolic blood pressure

Up to present, ergonomic research on geometrical design of forest roads has been mainly promoted by using either a radius of curve or a driving speed as a factor. In this study, however, we evaluated the geometrical design with two factors: a time required which a car got through a sight distance of a circular curve, and a difference between sight distances by calculation for braking and observation. We obtained the following facts with a high accuracy. A reduction of the time required and the difference in sight distance cause to increase a systolic blood pressure which indicates driver's psychological and physiological loads. Moreover, the systolic blood pressure presents a rapid increase in case of driving a curve of which the sight distance by observation is more than 5m shorter than that by calculation for braking. According to these results, we can advise that the sight distance by calculation for braking should be more than 5m longer than that by observation to keep driver's mental load in low. It becomes clear that the sight distance is an effective index with the radius of curve to estimate driver's psychological and physiological loads when driving at a curve. Moreover, the geometrical design of forest roads can be assessed more exactly by means of using the difference between sight distances by calculation for braking and observation. Besides, variation in systolic blood pressure, which could reflect the psychological and physiological load of a driver, was investigated in order to evaluate the geometrical design of forest roads from the viewpoint of driver's psychological and physiological response. Alignment description of a certain length section of forest road was experimentally selected for examining the evaluation method based on the driver's psychological and physiological response, which was not previously established. The interrelation analysis between the systolic blood pressure of examined drovers and the 9 patterns of alignment description was carried out for 13 road sections about 800m in length in present forest roads with different grades. It was concluded that the sight distance ratio was the best evaluation parameter through analyzing the following significant parameters; 1. The sight distance ratio (accumulated value of sight distance at various curve to length of road section) , 2. Curve length ratio 2 (the curve length summation of road section to the distance summation between intersection points) , and 3. Summation ratio of intersection angle (the intersection angle summation to length of road section). The systolic blood pressure only increased about 10mmHg when the sight distance ratio was 100% on the road. The systolic blood pressure, however, increased 40mmHg when the ratio decreased to 50%, which was not obviously suitable in the forest roads.