Safety investigators: fouled ballast, bad ties caused 2014 CN derailment

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Safety investigators: fouled ballast, bad ties caused 2014 CN derailment

What are the mileposts? I did not know subdivisions were xxxx miles long. The article states:Following the incident, Canadian regulators ordered CN to limit speeds and increase track inspections between Milepost 90.1 and " Milepost 1142.8" on the Fort Frances Subdivision.