Population expansion in a narrow peninsula. SF doesn't have room to expand really. It hits the Bay to the north, it hits the Bay to the east, it hits mountains and the Pacific Ocean to the west, and it hits other cities to the south. That aside, the best way to deal with commuter traffic would be a bypass, but there's no room for one unless you go over or under water. If you're far enough north (San Rafael or further) and going far enough south (or vice versa) you can just go around the Bay entirely, but even the 880, wide as it is, has bad traffic through Oakland and San Jose, and it's getting worse. Those areas CAN expand eastward, and they are, and the added population is clogging that freeway as well. I don't think I-5 is much better.

They want to reduce speeding? You can't stop everyone from speeding if people need to speed. What you have to do is take away people's need to speed. Public transportation is a good answer, but it's not good enough. If you ask a lot of people why they are speeding, many will tell you it's because there are consequences for arriving late. If you arrive late to work you can be let go, and the area is super expensive as it is. If you arrive late to an appointment, it gets canceled, and you have to reschedule. Pass a law criminalising penalties for being late. Take the excuse away. You're late to your job because you were driving safely and hit every stop light on 19th. Okay, no harm no foul. Also, does every damn job need to start at the same time? Break up the busy periods.