BALTIMORE (AP) — Federal and state officials and Amtrak are studying ways to improve a 141-year-old tunnel that carries passenger trains through Baltimore.

The two-track tunnel opened in 1873 and carries Amtrak, commuter trains and Norfolk Southern Railway freight trains through the city. Officials say it creates a low-speed bottleneck that affects more than 140 trains a day and impedes movement along the busy Northeast Corridor.

A $60 million, federally funded study on how to fix the tunnel began last fall. Officials announced Wednesday that it has entered a new phase that includes expanded outreach to the public. It’s expected to be complete by 2017.

In 2001, a freight train derailed in another aging Baltimore tunnel, sparking a chemical fire that paralyzed the city for days.

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