You are a bounty hunter tracking a fugitive on a bicycle. (Gas prices have hit everyone.) He may be headed south to the border or west to California. (But we know he is not going east or north.) You come upon the following two pairs of bicycle tracks through a slightly muddy part of a field:

Is it possible to determine which pair of tracks you should follow?
Specifically, can you determine whether the top set is a bicycle traveling east to west or west to east, and whether the second set is a bicycle traveling north to south or south to north?