Just heard that autosocks were better than chains for Prius in snow. True?

My first Subaru had very narrow clearance between the struts and inside tire sidewalls, significantly limiting chain choice. I ended up carrying an old set that fit the bare tires but was unlikely to be usable, but could be shown to the ossifers at any potential chain checkpoints.

In 17 years, never needed them, always flagged through checkpoints without question. Now with a newer Subaru with larger tires, I have a correctly fitting and usable set for it.

 

Although I have never driven in western states, I do remember driving on I-84 during Christmas time in the snow. I-84 I remember did not continue all the way to the west coast. Just realized I was on this Interstate 84 (Pennsylvania–Massachusetts) - Wikipedia
and Your I-84 is this Interstate 84 (Oregon–Utah) - Wikipedia

 

For folks looking to alternatives to tire chains for serious winter conditions, here is a description, including images, of six 'alternative traction devices' (sock-like and others) approved in Washington State:
http://www.wsp.wa.gov/traveler/images/traction/alt_traction_device.pdf