Simplify the following text for a Grade 4 native English-speaking person.
Original: In the late 1960s and early 1970s there were plans for a `` Picc-Vic tunnel '' to carry main-line trains under the city center , but this proposal was abandoned because of excessive cost .
Simplified: In the late 1960s and early 1970s there were plans for a `` Picc-Vic tunnel '' . This tunnel would carry main-line trains under the city center . .