This is my first post on this board

Our wedding is going to be one-hour away from our hometown, (most of the guests are coming from the same area). Because the wedding is far away, and also because we expect there will be a lot of friends who will be drinking, we wanted to book a guest shuttle to transport people from a 'park & ride' lot in our hometown to the venue, and then back. The bar will shut off 30 minutes before reception ends and then there's the hour drive back to sober up.....or they'll at least be within pickup or taxi range. So that we know what size shuttle, (or bus) to book, (cost varies considerably), we want to know how many people will want to use the shuttle. Some have said that they will probably just drive their own cars. Now my question...how do we get an RSVP headcount for the shuttle? Do we use a separate RSVP card within the wedding invitation or do we just add it is a line to the RSVP card? Any other tips or suggestions?? Anyone else had a similar experience with advice? Thanks in advance for your help.