I live in Contra Costa County, California. The libraries in this county work as a group, as branches. You get one library card with your signature, a barcode, and the a number. Most numbers I've seen start out "2 1901" and I've memorized my old library card number that no longer works (but I haven't memorized my current number!) My old number (don't bother trying, you'd need the last four digits of my phone number) was 2 1901 01362 5904.
Anyway, all of the CCC libraries I've been in have self-checkout machines, where it scans the barcodes on the book(s) and your card. In other words, dealing with a librarian just to check out a book is optional.