An analysis of supermarket checkout times has shown that express lanes (for people with fewer than 5 items, say) are not always the most efficient checkout route for time-sensitive shoppers.
Dan Meyer, a high school maths teacher, has done the hard work (providing his data and analysis) and came to the following conclusion:
[Express lanes] attract more people holding fewer total items, but as the data shows […], when you add one person to the line, you’re adding 48 extra seconds to the line length (that’s “tender time” added to “other time”) without even considering the items in her cart. Meanwhile, an extra item only costs you an extra 2.8 seconds. Therefore, you’d rather add 17 more items to the line than one extra person!
via Kottke