Is it possible to transport many (up to 12) bikes using some sort of auto-trailer?
Where I live it is common for commercial operator to purpose build trailers for carrying bikes such as these. 

The other option I have seen is custom bike racks for back of any flatdeck trailer or trucks.

One event here has over 1000 entrants to a relay - they need to transport 1500 bikes on the day, up to 100km..... So it's certainly doable.... I am glad I don't do their logistics planning...