To access some services including those departing from Atlantic Terminal, you must change the number of cars in your consist/train. 

1. Launch Train Sim World.
2. From the menu choose the Long Island Rail Road Route and then Timetable.
3. Choose either the M3 LIRR or the M7 LIRR.
4. Then click on Switch Livery.
5. Now choose between 10, 8 or 6 cars and press continue.
6. Services departing from Atlantic Terminal will require a 6 car consist.
7. Now you will find many more additional services to drive.