If you're looking for a quick fact to explain congressional gridlock, it's this: In the 113th Congress, only 59 members have voted with the majority of their party less than 90 percent of the time (20 Republicans and 39 Democrats).So first of all, a minor point: "Congress" here apparently means the House.
Second: polarization -- partisan polarization -- just means that Members vote with their party and against theother party. Gridlock is about failure to pass legislation. Indeed, really more specific; to go back to the traffic analogy, it's about failure to pass legislation that everyone wants, but is being blocked by collective action failure of some type.
Which is to say that gridlock and polarization are not the same thing, and not necessarily related in any straightforward way.
Indeed, within the House, partisan polarization should ease gridlock. Since the House runs by majority party, if that party is unified, then they can basically do whatever they want.
Thus in the historic 111th Congress, in 2009-2010, the House was extremely productive. Very strong polarization, and no gridlock at all.
The Senate, with the filibuster forcing supermajorities, is another story; there, polarization might make gridlock more likely assuming that the majority party has fewer than 60 Senators. However, with 60 Senators, and given unified government, polarization should mean less, not more, gridock.
What about with divided government? Does polarization then mean gridlock?
Not necessarily. A non-polarized Congress can avoid gridlock by having different majorities express themselves on different issues. On the other hand, a non-polarized Congress also can create a lot more gridlock. After all, a polarized Congress means that one person can bargain for her whole party; a non-polarized Congress can devolve into an ungovernable mess (indeed, one theory of why parties exist at all is that legislatures don't really work well without them).
In other words, the relationship between polarization and gridlock is complicated.
What does cause gridlock, however, is a party driven by aversion to compromise -- both internally and with the other party. That's what's happening now, with the dysfunctional GOP. And that, not polarization, is most likely the primary source of current gridlock.