The Metropolitan Transportation Authority needs to spend more than $7 billion in additional funding to improve its aging and increasingly unreliable subway fleet in New York City, according to a new report by a local watchdog group.

The nonpartisan Citizens Budget Commission said in the report released Wednesday that subway cars have been breaking down more frequently as the MTA has replaced cars at a slower pace and lengthened maintenance cycles. Increasing the subway system’s reliability will require the restoration and replacement of much of the fleet, and will cost more than $9 billion, the report said.