On Mondays and Tuesdays, the day's mileage was increased to 195½ by a trip from Lewes to Berwick and back. This additional mileage provided the only instance of a non-revenue journey, as the "motor" returned empty from Berwick to Lewes.
Source: wiktionary
The second strategy is to develop specific care and maintenance rules that will need to be strictly followed by the system operator - including the use of specialised machines to clear the permanent way of snowfall, to de-ice the rail grooves and the running of non-revenue services at night to prevent ice formation on the OCL [overhead contact lines].
Source: wiktionary