The Port Authority Bus Terminal in Midtown Manhattan is a major hub for commercial and commuter bus lines serving New York City. Getting to Grand Central Station from Port Authority is easy and you have options, but one is better than the others if you're looking to save time and money. Rather than hailing a cab or walking a full mile down busy 42nd Street in the elements with your luggage, take the underground shuttle train from nearby Times Square.
Go to the lower level of the north or south terminal buildings. Both buildings have a one-block-long underground passageway that connects the Port Authority terminal to the Times Square station of the New York City public transit system (the MTA). The passageway is well-lit and usually busy with people, even during off-hours.
Follow the MTA directional signs for the Grand Central shuttle, marked by a gray circle with a white S in the middle. Signs may also read "42 Street Shuttle." MTA directional signs are prominent leading from Port Authority up to and throughout the Times Square station, displaying letters and numbers for multiple trains inside colored circles. Keep your eyes on that gray circle with the white S until you reach the ticketing area of the station.
Purchase a MetroCard or a SingleRide ticket to get through the turnstiles and on to the train platform. The MetroCard is best if you're going to be using the MTA transit system frequently while in town, as it's a value-added fare card with discounts for multiple trips. The SingleRide ticket is best if you want to get from Port Authority to Grand Central and won't be using MTA transit after that.
Use your card or ticket to enter through the turnstiles and on to the train platform. The shuttle runs directly to Grand Central, with no stops in between. If it is late at night or early in the morning (generally between midnight and 6 a.m.) the shuttle may be out of service and you will have to take the Number 7 train (purple circle with a 7), which runs at all hours and makes a stop at Fifth Avenue before reaching Grand Central.
In the rare occurrence that the subway system is down, take the MTA's M42 crosstown bus from the north terminal building to Grand Central. This option will take longer, as the bus makes many stops along the way.
For first-timers to NYC, Port Authority, and Midtown in general, can be overwhelming. Information booths are located in each Port Authority terminal building to help you get your bearings.