What is the gap provided between two rails for free expansion due to temperature changes?

The correct answer highlights the importance of thermal expansion in railway engineering. The gap provided between two rails serves to accommodate the expansion of the rails as temperatures rise. When temperatures increase, materials such as steel expand, and without a sufficient gap, the forces generated could lead to buckling or other structural issues in the railway track.

The standard gap recommended for this purpose is typically around 15 to 30 millimeters, depending on various factors such as the specific rail type, climate conditions, and track design. The choice that identifies a gap of 15 to 3 mm appears to reflect a misinterpretation of the correct range, as it does not align with the typical thermal expansion gaps used in practice. Ensuring that the gap is neither too small nor excessively large is crucial for maintaining track integrity and safety.