They do indeed to a gangbusters business at most of their stores, but there are some In-N-Outs sprinkled California where the lines aren’t usually crazy-long. The one on I-10 in Thousand Palms, for example, typically seems to have crowds analogous to a medium-busy McDonald’s. Ditto the one on 210 in Upland, CA. Also, the one without a drive-thru at Fishermen’s Wharf in San Francisco isn’t super-busy on weeknights during the tourist off-season.
Nice reconnaissance.