Gauge length:
The gauge length of a railway track is the distance between the inner sides of the rails. It is an important factor in determining the maximum permissible speed on BG (Broad Gauge) railway tracks. The gauge length affects the stability and smoothness of the train movement. If the gauge length is too narrow, it can lead to derailments and accidents at higher speeds. Therefore, a sufficient gauge length is necessary to ensure safe and stable train operations.

Degree of the curve:
The degree of the curve refers to the angle subtended by a circular arc of a railway track. It is measured in degrees per unit length (usually per 100 feet or 100 meters). The degree of the curve affects the lateral forces acting on the train and its stability while negotiating the curve. Higher degrees of curves result in increased centrifugal forces, which can lead to derailments at higher speeds. Therefore, the degree of the curve is an important factor in determining the maximum permissible speed on railway tracks.

Ruling gradient:
The ruling gradient refers to the maximum allowable slope or gradient on a railway track. It is the steepest gradient that a train can safely traverse without losing traction or causing excessive wear and tear on the track and rolling stock. The ruling gradient affects the tractive effort required to climb uphill and the braking effort required while descending. Steeper gradients limit the maximum permissible speed due to the increased power requirements and reduced braking efficiency. Therefore, the ruling gradient plays a significant role in determining the maximum permissible speed on BG railway tracks.

Maximum allowable superelevation:
Superelevation, also known as cant or banking, is the process of raising the outer rail of a railway track on a curve to counteract the centrifugal forces and provide a more comfortable ride for passengers. The maximum allowable superelevation is the maximum amount by which the outer rail can be raised. It is determined based on the design speed, lateral acceleration limits, and the track and rolling stock characteristics. Excessive superelevation can lead to instability and derailments, while insufficient superelevation can cause discomfort to passengers. Therefore, the maximum allowable superelevation is an important factor in determining the maximum permissible speed on BG railway tracks.

Conclusion:
In conclusion, all four factors mentioned - gauge length, degree of the curve, ruling gradient, and maximum allowable superelevation - are crucial in determining the maximum permissible speed on BG railway tracks. Each factor affects the stability, safety, and comfort of train operations. Therefore, considering all these factors together is essential to ensure safe and efficient train movements on railway tracks.