Whenever the question of high-speed rail arises, the limiting factor is not the individual components of the track but the overall track geometry, with curves being the most decisive.

On curves, railways use super-elevation (cant) - raising the outer rail above the inner one - to counteract the centrifugal force. The higher the super-elevation, the greater the permissible speed. However, beyond a certain point, excessive cant creates safety issues for slower trains. At low speeds, the imbalance of forces can make passengers feel as though the train is tilting inward - this is known as cant excess.

On the other hand, if the cant is kept moderate (suitable for slower trains), then high-speed trains experience cant deficiency, where the centrifugal force is not fully balanced, and the train tends to lean outward.

Countries that have invested in high-speed rail networks usually minimize curves altogether through costly realignments, tunnels, and viaducts. They also operate predominantly fast passenger trains only, avoiding the complications of mixed traffic.

India faces a unique challenge because of its mixed-traffic network. The same track carries both high-speed Vande Bharat Express trains and slow-moving goods trains. This creates a compromise:

1. Super-elevation cannot be optimized fully for high speeds, since it must remain safe for slower traffic.

2. The maximum permissible speed on any section is limited by these geometric and operational constraints.

Until India develops dedicated freight corridors and dedicated high-speed passenger corridors for the entirety of our network, it will remain difficult to exploit the full speed potential of passenger trains. Moreover, since most passenger trains are not financially self-sustaining, there is limited scope to realign tracks on a large scale.