1 in 12 turnouts means that for every 12 turnouts, there is one turnout that did something or is special in some way. 1 in 8.5 turnouts means that for every 8.5 turnouts, there is one turnout that did something or is special in some way.
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Speed over 1 in 8.5 turnouts is 10kmph, and 1 in 12 turnouts is 15 kmph. In case of curved switches it is 15 kmph for 1 in 8.5. For 1 in 12 turnouts with PSC sleepers the speed can be increased to 30kmph with spl.