It's a bureaucratic hack. Some states have laws that state that bills can't be voted on unless they've gone through a committee or that bills can only be introduced at the beginning of a legislative session (the beginning of the year) and not the end. This way the bills can be honestly and properly debated on. So this transportation bill was already in process and up for debate. Bills can always be "amended" - so they "amended" the bill by adding their vaccine mandate language and removing what was originally there so they can ramrod their legislation through.