What is the relationship between Northeast corridor and Amtrak in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

Gardner told lawmakers that it would cost Amtrak $1 billion per year just to keep its Northeast corridor infrastructure in a state of good repair, and would cost another $4 billion per year to complete its backlog of projects on the 457-mile corridor, a span that includes numerous century-old bridges and a 142-year-old tunnel.

Answer: operator