Any cities in Germany or the rest of Europe that are similar to San Francisco in size and density? SF seems relatively really decent for transit and walking

You seem to misunderstand density. In my town in Germany I can walk to anywhere I need to go in 30 minutes, and in 50 I can walk from one end of town to the next. I'll pass dozens of bus stops and 3 train connections.

If I walked that same distance where I grew up in the US I'd be at a gas station, a church, or the woods. None of these offer adequate pay for me to live. I'll pass 0 bus stops, nearest train station would be about 20 miles away still.

This is why Americans freak out about gas prices. There are no other options in many places. Some people will read that and say "just move", but that fails to acknowledge the ongoing housing crisis.

So anyway back to the point on average Americans have to drive further and more frequently just to live. In Germany driving is generally more of a choice, at least in my experience, and due to the general density of cities you don't even have to drive far. Which helps with the gas costs.

If it were as expensive as Germany, your average commute would be significantly shorter

In the long run sure, but in the long run we're all dead.

I did carpool with a friend often for the first few semesters, however that eventually didn't work out due to different work and school schedules. I often left class and drove straight to work. The days I didn't work I'd stay in the university library till 11pm doing work. I did have some off days of course, but still long days were common.

It also took just under 2 hours as it was mostly a rural stretch of interstate. Which helped a lot with gas efficiency at least. My car was also small and gas efficient so it was about 2.5 gallons per day.

If we round up to 3, that would be about $384 a month at the $8 per gallon price. Which was significantly cheaper than a room in an apartment. Those averaged around $450 to $500, but due to a lack of transit in the city I would still be driving to school. Plus you have to account for semester breaks where I wouldn't be driving at all. Of course gas was ranged from $3 to $3.50 per gallon then.

But then again I knew a guy who did this commute in a pickup truck. He complained about gas daily.

Also many of these people were just people I knew, not friends per se.