The Seattle Marathon is Sunday and while the course isn't on Capitol Hill for most of its route, it does encircle us and can make it difficult to get off the Hill or back to it. (But why would you ever leave?)
Miller Park Blog has a few tips for anybody out for a Sunday drive:
Going north on 23rd to the University District or getting to I-5 via the Roanoke onramps won't work. Accessing I-5 via Madison, Denny-Steward-Yale (southbound) or Olive (northbound) will work.
Here's a map of the course:

Roads will be closed early for the 7:15a start -- site says all roads will be opened by 2:15p.
As far as rooting and support go, Capitol Hill is a low responsibility zone. It's not our marathon! You'll note that the course pretty much avoids most of the Hill proper -- only the last few miles bounce along the top of the St. Mark's region. So, if you wanna rep the Hill, stand at the C point in the map below.
That's around the mile 23 mark in the race (mile 10 for the half-marathoners). By that point, those runners will need your support.