My first thought was if you hit the Greenwich meridian then you are going west. However when I thought it about it more, I realized that's not right, because you can be "west" of Greenwich meridian and still be heading east.
I think once you started heading East you will always be heading East, just because of the direction you are facing. A person can be going West and past you, but they would be heading in the opposite direction. It would be similar to going around a block, One person only makes right turns around the block, the other only left turns, they will pass each other, but facing opposite directions.
at 9:21 AM on Aug. 7, 2010