For only the second time ever, the MTA says it might have to shut down the entire system, depending on just how powerful Sandy turns out to be. NY1's Tina Redwine filed the following report.

What will it take to shut down the buses and subways?

The MTA says sustained winds in excess of 39-plus miles per hour will bring the system to a halt. Low-lying areas like Lower Manhattan are particularly vulnerable.

Right now, Sandy is predicted to bring sustained winds of anywhere from 30 to 50 miles an hour when it hits.

The MTA is doing several things to prepare. Crews are inspecting and clearing main drains and pump rooms. Trains and buses in flood-prone zones are prepared to move to secure locations to keep them from suffering water damage that could slow the system's return to full service. Employees are checking and readying pumps and emergency equipment in case they're needed.

The MTA says it will open its Incident Command Center Sunday morning. A customer advocate will be there to represent the interests of riders as decisions are made on possible service cuts.

The position was created after the Christmas blizzard of 2010 and was in place during Irene last year, when the MTA shut down service as a precaution for the first time ever.

The MTA also controls seven bridges and says one or more of them may be closed to traffic if sustained winds hit 60 miles per hour.

As for the subways and buses, the MTA says riders will get ample notice if it has to shut down the system.