When two rails meet, the way they’re joined can shape the strength, longevity, and safety of an entire track section.

Most people assume a train should be perfectly balanced on a curve—tilted just right, riding equally on both rails. But that only works for one train, at one speed. On real railways, things aren’t that simple. Enter cant deficiency.

Every train, whether carrying passengers or freight, is guided by a surprisingly small area of contact: the wheel–rail interface.