[What you need to know to start the day: Get New York Today in your inbox.]

Even when there are no subway delays, it takes Amy Sacks at least an hour and 20 minutes to get to work in the Bronx.

The problem is that the subway still leaves her about a mile — and a bus ride away — from her office. “There’s always a transfer unless I use my feet for the second half,” said Ms. Sacks, a writer who lives in Manhattan.

But the key to a shorter, easier commute lies just outside her office door: railroad tracks that run through the Bronx.

The tracks are used by Amtrak trains, but would be opened to new commuter trains under a billion-dollar expansion by the Metropolitan Transportation Authority of rail service linking Manhattan with suburbs north of New York City. Four new train stations for the Metro-North Railroad would be built along the line in the eastern Bronx, where subway service is sparse and buses are often slow and unreliable.