Read this: A railway electrification system supplies electric power to railway trains and trams without an on-board prime mover or local fuel supply. Electrification has many advantages but requires significant capital expenditure. Selection of an electrification system is based on economics of energy supply, maintenance, and capital cost compared to the revenue obtained for freight and passenger traffic. Different systems are used for urban and intercity areas; some electric locomotives can switch to different supply voltages to allow flexibility in operation.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): How do some locomotives function in order to be more flexible in operation?
can switch to different supply voltages