I didn't realize chains were a requirement with a 4x4.
Anyway, the CHP just seems to close the roads and leave people stranded whenever there's snow.
In R3 conditions chains are required, no exceptions. But, CalTrans does tend to close highways before conditions get that bad. (Local areas can have their own rules.) I know plenty of people who have spent the night on I-80.
For R2 conditions, if you have 4WD and "M+S" or 3-peak-snowflake tires you're good to go but have to carry chains or "tire traction devices." I think compliance with this is probably low. CalTrans has never stopped and checked me for this. My guess is that it does happen now and then, particularly on roads like Glacier Point Road in Yosemite where CalTrans is really conservative (since a ton of drivers there are from out of state).
I've never seen the highways up in the mountains open in R3 conditions. Caltrans/CHP play it safe and shut down the roads. People can barely drive safely in R2 conditions. R3 would be a disaster.
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