Many of us have not ridden in a while. More people are on their PDAs than ever before. Before you challenge a car and switch lanes or cut accross do the following:
1. slow down
2. make eye contact with the driver
3. have verbal or non verball communication with the driver which confirms that the driver gives you permission to do whatever you're trying to do
4. pray that you understood what you think the driver gives you permission to do
5. If all of the above fails, wait for traffic to clear and drop to the back and then do what you have to do.
In any event, stay safe, think smart and assume nothing. For more safety tips, downloat my book that is free on this site.