Yes, there are three levels of the amount of “empty cabins” that get sent from the Caribbean Beach station to Riviera. Same way from Epcot to the Riviera station. All pending on the amount of people traveling in each direction.
They will also fill cabins as they come through if it starts backing up. Just like a boat, bus or monorail, it is public transportation and at busy times you will sit with other people. But, unlike a bus or monorail, everyone is seated and there is nobody standing up two feet in front of your nose.
All lines are five minute journeys from point A to point B, except the ride from Riviera to Epcot and Epcot to Riviera which is approximately 8 - 10 minutes.
It is also a requirement that shirts and shoes must be worn at all times.