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 discussion 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. Bridge generally consist of superstructures such as beams and trusses, and substructures such as piers, abutments and foundations.
In any case, the time elapse since construction, traffic volume over the railway line, types of materials, maintenance conditions and environmental changes produce significant differences in current strength of bridge. 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 current 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 on rail-road level crossings 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 railway and road passage at conventional level crossings has hindered track maintenance and, in particular, resulted in the serious problem of increasing collision accidents.
On the other hand, viewed from the road standpoint, in addition to increased automobile accidents, traffic is temporarily cut off while trains pass and automobiles must stop before entering crossings, resulting in traffic congestion.
Therefore, the following policies are being actively pursued in Japan with government assistance.
