It's quarter past two in the morning. Charlie's wife stands alone in the Scollay Square subway station clutching a cold pastrami sandwich. She hears an oncoming train. She winds-up to throw. But with a wooosh the train has come and gone at 70 m.p.h. Russian dressing oozes out onto the still-trembling tracks.

The Massachusetts Bay Transit Authority (MBTA) is installing 76 gleaming new aluminum subway cars on its Harvard-to-Ashmont "Red Line."

The cars, costing $15 million, will supplement the familiar, dirty-blue cars now plying the MBTA tracks and will help handle the additional traffic when the Red Line is extended south to Quincy later this year. They can go up to 70 m.ph.-15 m.p.h. faster than the old ones.

"The Authority is very pleased with the new cars," said MBTA general manager Leo J. Cusick. "And incidentally, these cars are the first aluminum transit cars to be built in United States."

A notable feature in the new subway cars is the seating arrangement. Rather than sitting on plastic benches along both sides of the car, riders will relax in black vinyl-upholstered seats positioned in rows, much like those in regular trains.

The cars have large tinted windows, and a public address system which announces each stop. But they don't announce Scollay Square because it's now called Government Center, and besides, the new cars don't go there.