deteriorate. Recently, attention has been given to the close relationship between train running and track maintenance as seen by new track deterioration theories which incorporate this phenomenon.
Various improvements are being made to prevent this problem in conjunction with strengthening tracks. These measures include installing side ditches and drains, ensuring passageways and spaces to place materials for maintenance and track patrols, and particularly for weak roadbeds, improving roadbeds and laying ballast mats.
From the perspective of disaster prevention, care must be taken to repair and construct new slope protection, rock fall prevention and bank protection structures in consideration of the constantly changing environment. There is a Japanese proverb which states that "Disaster strikes when least expected." In particular, care must be taken when deforestation, factories, residential land and other developments are to be carried out nearby, and talks should be held with developers from the early stages.
4.2 Bridges
Bridge structures are designed through dynamic theory with a fixed safety factor added in consideration of load conditions. Bridges generally consist of superstructures such as beams and trusses, and substructures such as piers, abutments and foundations.
In any case, the time since construction, traffic volume over the railway division, types of materials, maintenance conditions and environmental changes produce significant differences in load bearing strength. In terms of disaster prevention, bridges range from those for which speed restrictions or other measures have been implemented because they are already considered dangerous to those which are still in excellent condition even 100 years after their construction.
There are also considerable differences between the technologies at the time of construction and current technologies. Therefore, it is of prime importance to carry out surveys using current technical ability to understand the present situation. In Japan, a method for automatically calculating the load bearing strength of bridges by measuring the vibration and deflection when trains pass over has been developed, and this method is used for bridge control and judgment of propriety of higher speeds.
4.3 Intersections with Roads
For better or for worse, motorization is an inevitable consequence of social and economic development. Although quite troublesome from the viewpoint of railways, road transport nevertheless plays an important social and economic role.
Railways are characterized by the fact that they cannot stop suddenly, and have therefore asserted and maintained the right of way at crossings since their origin. However, increased
