Why some queues feel much slower even when they move at the same speed

Two supermarket queues seem to have the same number of people and move at roughly the same speed. Somehow the one I choose always feels slower. I suspect waiting without knowing when you're next is worse than watching a predictable process, and that I notice every delay in my own line while ignoring the others. Is there research about perceived waiting time versus actual time, or is this mostly selective attention?