CSX owns the tracks on MARC’s Brunswick and Camden Lines. CSX issues a heat order for operations between 1 pm and 7 pm if the predicted high temperature for the day is 90 degrees or higher, or if there is a large predicted change in temperature (e.g., 25 degrees or more), especially if the predicted high temperature is higher than 85 degrees. Large predicted changes in temperature are usually the reason for heat orders in the fall or spring.
If CSX issues a heat order, passenger trains must go 20 miles per hour below the maximum authorized speed, but not less than 40 miles per hour. Freight trains must go at least 10 miles per hour below the speed limit, but not less than 30 miles per hour. On the Brunswick and Camden Line tracks, under normal operations, the maximum authorized speed is 79 miles per hour for passenger trains and 60 miles per hour for freight trains.