Curved sections involve similar measures as with straight sections, and suffer from a number of additional problems.
(1) Curve Radius
As described earlier, speed restrictions along curves can be eased under current conditions by improving cars.
The table on the following page shows the results of a comparison of when the existing 400 m minimum curve radius is improved to 800 m and when the curve radius remains the same, but the running speed is increased by 15 km/h due to car improvements, over a double-track section roughly 350 km in length.
In this case, car improvements is far more advantageous than implementing improvements to curves.
Comparison between Improvements to Curves and to Rolling Stock
(2) Transition Curves
The length of transition curves is determined by both safety with respect to derailment and riding quality.
Regarding safety, if a changing rate of cant over transition curve is too large, it causes a large unbalance of wheel load among 4 wheels of car bogie, increasing the possibility of derailment for wheels. Normally, the transition curve length is set at between 600 to 1000 times the cant.
