I choose my route to avoid freeway onramps and exits. People drive way to fast here while they're acclimatizing to a different speed limit. If you want to get nailed by an impatient driver, bike around on and off ramps...

If you can't avoid them, it really depends on the design of the individual interchange. Usually there's a lane for cars who want to go by, but not get on the freeway. I take that lane, if there isn't a better road for me.