Constant lateral acceleration due to unbalanced centrifugal acceleration may occur along curves. However, this is not a problem as long as speed restrictions imposed for reasons of safety are observed.
More of a problem is the degree of changes over time for unbalanced acceleration. This can be determined looking at the relationship between transition curve length and train speed.
(2) Track Distortion and Train Vibration
Except in the case of self-excited vibration such as hunting movements where the problem lies with the train, train vibration is closely related to track distortion. In addition, this vibration increases in proportion to speed.
The relationship between track distortion and train vibration can be calculated through a vibration analysis simulation using a dynamic model. Findings showed that there is insufficient correlation between track distortion over 5 m or 10 m spans and the train vibration of high-speed trains, and that there was greater correlation in the case of track distortion with a longer wavelength. This was also proved through measurements.
2.3 Track Deterioration
Excluding tracks with special structures, dynamically speaking, tracks are incomplete structures with the earth roadbed and ballast as a foundation. Track performance must be sustained while restoring gradually increasing deterioration caused by trains through maintenance work. The main type of track deterioration is ballast sinking. Ballast sinking after maintenance work has been performed generally progresses as shown in Fig. 3, and is a cause of track distortion. The speed at which track deterioration advances is closely related to the structural strength of the track and the damaging force of the train load.
In Japan, track deterioration coefficient △ which quantifies the speed at which deterioration advances in relative terms can be defined as follows:
