Photo by Robert Couse-Baker.
The reason lane 13 is almost always faster is, as you probably guessed, superstition. Since others avoid that lane, it may be a lucky one for you.
We've previously mentioned one of the other tips for choosing the fastest checkout line: avoid the express lane if there's a shorter line elsewhere, even if people on that line have more items in their baskets. Each customer adds 48 seconds to the transaction, compared to 2.8 seconds for each item. Gigabiting says the breakeven for when you would choose the line with the extra person is about 17 items.
More checkout line rules are offered in the link below. How do you get out of the supermarket faster?