The Interstates are the only ways across the river without adding 100+ miles to your route. The I-5 Interstate Bridge has sidewalks. The I-205 Glenn Jackson bridge has a bike lane. No biggie. (well except when you encounter Interstate Bridge salmon like I mentioned in my ride report. Die, salmon, die!)

I've done Centuries and Metric Centuries that are at least 95% freeway miles. Sometimes it's the only reasonable way to go.