Express lanes can be separated lanes with fewer exits that allow you to go faster because of fewer lane changes. Chicago (and I'm sure many other cities) have these. They're separated by concrete barriers and only have exits every couple miles, so you'll be right next to super slow traffic while you're doing 20+ MPH more than the "free" lanes. In Chicago, you don't have to pay to go in them, but here in LA, they have High Occupancy Vehicle lanes that you can use if you have more than one person in the, OR if you pay for using the lane with the FastPass you use for paying for other tolls.