What is the difference between blue ATVO bus and ACTV bus? Vaporetto passes cover the latter (according to Venice 2008 guidebook; can I buy a 24-hr vaporetto/bus pass at the airport before I get on the shuttle?
The ACTV is a Venice city bus. As such, there may not be any overhead luggage racks. This bus comes into space A1 at the Piazzale Roma. Your vaporetto pass should cover this bus. The ATVO bus is more of a private bus system. It's a bit more expensive but I understand that they have overhead luggage racks. This bus comes into space D2 at the Piazzale Roma. I don't think that your vaporetto pass would cover the cost of this bus. You may be able to buy the vaporetto pass at the airport. I'm not sure.
The orange ACTV bus is operated by the same folks that run the vaporettos. So your ACTV pass will work on the ACTv bus. You can buy the pass at the airport. The bus picks up at the front of the airport terminal in the arrivals area. Ground level. Just stick your ticket into the yellow stamping machine near the stop. That will validate it with a time stamp. It will be good from that time until the oass expires. 24 Hr pass stamped at 10 am would be valid until 10 am the next day. This bus is a local so it will have more stops and may take 5-10 minutes longer to get to P. Roma. There are overhead luggage racks inside the bus.
The blue ATVO bus is an express bus that is not operated by ACTV. Similar to the airport shuttles you're used to in the US. No stops until you get to P. Roma. Cost 3euros per person last September. It has small overhead racks but the main storage is under the passenger compartment and is accessed from the outside. Takes about 20-25 minutes to get There.