The maximum speed of trains is subject to restrictions along curves in accordance with the curve radius. This is a specific safety measure against the overturning of trains.
Specifically, trains overturn if the combination of motive power and centrifugal force imposed on the cars acts outside the tracks. Therefore, the restriction is determined taking into account a safety factor of three to four times.
Predetermined cant has some bearing on the speed restriction. However, it is, in itself, limited by the problems of overturning on the inside of curves when stopping and riding quality when faced with cant fluctuations.
In general, the maximum speed restriction on top class trains is being eased recently, thanks to a calculation method taking into account car spring effect, vibration, wind pressure and other factors.
(2) Derailment
Derailment occurs when the ratio of wheel load and lateral force acting between the wheels and rails exceeds a certain limit (normally 0.8) for a specific period of time. As a result, it is dangerous when there is a simultaneous decrease in wheel load and increase in lateral force due to reasons such as car vibration. Track alignment on curves is a major controlling factor, and sudden changes in cant reduce wheel load.
Another type of derailment is when widening of the gauge causes the wheels to fall inside the tracks. This is caused by a lack of lateral strength of track, and the only remedy is to increase it.
2.2 Riding Quality
Riding quality is a psychological and physiological reaction of passengers. It varies significantly according to the individual and conditions, and is difficult to judge in quantitative terms. In Japan, a riding quality limit route map compiled by statistically processing the views of numerous passengers and measured values for vibration is used as a basis for evaluation using the vertical limit value proposed by Janeway as reference. (See Fig. 2.)
The appraisal of riding quality based on the coefficient is done as follows;
