WASHINGTON — Metro’s oldest cars, which investigators have determined to be unsafe in the event of a crash, and a batch of breakdown-prone middle-aged cars will no longer carry Metro riders after the end of the month.

Some of the original 1000 Series cars and the middle-aged 4000 Series cars will remain in Metro rail yards as scheduled for a few more months until each can be trucked out, but Metro announced Wednesday that the cars would no longer be used after July 1.

Metro is able to make the change now, rather than after more new 7000 Series railcars arrive, in large part due to service cuts that begin June 25. With shorter service hours and less scheduled rush-hour service, Metro will need fewer railcars each weekday.

The National Transportation Safety Board has long recommended Metro remove the original 1000 Series cars from service, since they can crumple in the event of a crash.

Metro made the decision to also retire the 4000 Series, since those cars often have door or brake problems. The cars never got complete maintenance overhauls.

Metro will maintain the system’s first pair of cars — numbers 1000 and 1001 — for historical purposes.

Other cars will be used for fire department training, store kiosks or scrap.