The distinction between the two is that while the Jewish Roadblock is done on purpose and with every intent of slowing down every body else on the road, the Polish Roadblock is done on accident and without the blockers knowledge.
A good indication of which one you're experiencing is the reaction you get when you flash your high beams at one of the offenders. If after repeated flashings, the offender does not move over, then it is most likely a Jewish Roadblock.
<one car moves>
<offending driver does the "My Bad" wave>
Okay, I'm not as pissed now, it was only a Polish Roadblock.