This is for our transportation/directions enclosure. Please edit for clarity, niceness and concise-ness? Is that a word? 
....Also, our hotel/church/reception are all within a 3 mile radius in downtown Chicago. Our reception goes very very late, so guests will be departing at different times. We have the shuttle to get guests there, but is it rude to indicate they can get home on their own by taxi? Our venue mgr will help us call a queue of cabs so they won't have to wait....???
"All guests are invited to take advantage of our free shuttle on Saturday. If interested, please meet in front of the JW Marriott at 3:30pm. The last shuttle will depart promptly by 4:00pm. This service is open to all wedding guests, not limited to those staying at the hotel.
The shuttle will take you to the church for the ceremony, and then on to the reception. We will provide contact information for local taxi companies for anyone needing a ride home at the end of the night."
Thank you!