Simplify the following text for a Grade 11 native English-speaking person.
Original: Able to operate from 25 kV overhead line current collection only , the fleet works outer-suburban services on the Strathclyde Passenger Transport rail network in Central Scotland .
Simplified: Able to operate from 25 kV overhead line only , the fleet works inner-suburban services on the Strathclyde Passenger Transport rail network in Central Scotland .