The FRA requires alignment to be measured with what lengths of chords for curved track?

The requirement for measuring alignment on curved track with specific lengths of chords is founded in the need for precision and consistency in ensuring track geometry is conducive for safe train operations. By using a 62-foot chord, you can evaluate alignment on larger curves, ensuring that any deviations can be detected over a significant distance. In many cases, especially for tighter curves or specific classes of track, a shorter 31-foot chord is also utilized. This flexibility allows for more granular measurements on curves that might not be effectively assessed with a longer chord. Therefore, the adoption of both chord lengths enhances the ability to accurately maintain and inspect track alignment, ensuring the safety and efficiency of rail operations.

The other choices do not account for the necessity of measuring with both lengths or suggest an incorrect standard applicable for all tracks. A singular focus on just a 62-foot chord would miss important assessments on tighter curves, while a standard only requiring a 32-foot chord fails to provide the comprehensive examination necessary for effective alignment measurement across different classes of railways.