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Installing modern subway signals along the perpetually crowded Lexington Avenue line in Manhattan. Adding elevators to 70 stations in a system where only about a quarter of the stops are wheelchair accessible. Extending the Second Avenue subway north to East Harlem.

These are some of the key pieces of the Metropolitan Transportation Authority’s new $54 billion blueprint to overhaul the subway and the rest of the city’s floundering transit network.

On Monday, transit leaders released their proposal for the agency’s largest ever capital plan, a critical document that offers a wish list of projects to tackle over the next five years.

The price tag might seem stunning — it is $20 billion more than the last capital plan — but it reflects an aging system with immense needs, from the subway and buses to commuter railroads.