To St Charles By Road
There really are not bike-friendly roads around the airport. If you must bike, we recommend taking the MetroLink to Forest Park, and then biking from there
(see biking from the Katy Trail to Forest Park and Downtown
). You can roll your bike onto the MetroLink trains.
It's about 20 miles from Forest Park to the Katy Trail.
If you insist on biking from the airport to the Katy Trail, here is Google Maps' recommended route