(almost?) all US state highways do, yes

Yes, the US tends to call them HOV (High Occupancy Vehicle, or Human Ordinance Vehicle) lanes, and they’re typically denoted by a large diamond painted along the center of the lane. Usually the far left lane on the highway, so it’s even past the fast lane. It often has limited entry/exit, and is often a double-solid white lane marker, meaning you’re not allowed to enter or exit the lane except at specific points. Sometimes there are even soft barriers, to further deter people from entering/exiting except at the designated points.

It’s a lane that is reserved for moving people rather than cargo; You’re only allowed to travel in if you have more than one person in the car, or are on a motorcycle. The theory is that by restricting specific lanes to carpoolers, you’ll encourage more people to carpool and have fewer cars on the road. And by restricting lane changes, you avoid slowdowns from people entering/exiting the lane. You typically only see them in major metropolitan areas with lots of commuter traffic.

In reality, it’s one of the most commonly broken traffic laws, with commuters often camping in the HOV lane even when they’re by themselves. Or people attempting to use it as a faster version of the fast lane. It is typically only a minor traffic ticket if you get caught. So enforcement is often very lax, and cops will often only pull you over for it if they’re looking for an easy ticket.

This comic is referencing a lady was pulled over in Texas, and cited for being in the HOV lane without another person in the car. She argued in court that she was pregnant, and since Texas considers fetuses to be alive, the court had to dismiss the ticket because she had a second person in the car. The judge ruled in her favor, mostly to avoid creating a major challenge to written laws over a minor traffic ticket.

What's a carpool lane? Do we have them in Europe?