Two-third rule than freight trains. On such tracks, the two-third rule applies to freight trains. The two-third rule means that the speed limit for a freight train is generally about two-thirds of the speed limit for an EMU. For example, the Dartford Loop Line has a speed limit of 60 mph for EMUs between Lee and Crayford. A freight train on this track is therefore limited to two-thirds of 60 mph, i.e. 40 mph. Two-third rule Two-third rule is British railway safety rule. For safety reasons, speed limits are imposed on trains running on a railway line. Many factors can affect the
Ladder of thirds Ladder of thirds A ladder of thirds (coined by van der Merwe 1989, adapted from Curt Sachs) is similar to the circle of fifths, though a ladder of thirds differs in being composed of thirds, major or minor, and may or may not circle back to its starting note and thus may or may not be an interval cycle. Triadic chords may be considered as part of a ladder of thirds. It is a modal frame found in Blues and British folk music. Though a pentatonic type, the melodies come "into being through piling up thirds below and/or above a