Attached are detailed routes that would be a nice ride for students to take to the Kickapoo rail trail. At the moment, I have just provided the Google map directions.

WEEKDAYS:

Basically, the 5 E Green line runs from the Illini Union to the bus stop Main & Brady, in Urbana (EAST&WEST). When you get on at the Union, you'll stay on the same bus for 45 stops(~30  min ride) until reaching Main& Brady. From the stop, it is a 4 minute walk to the trailhead. 

You must not take the 5 Green-Express as it does not reach that far east. This runs just about every 30 minutes. This exact route runs from ~8AM - ~7PM and is the same there and back

WEEKENDS:

Boarding at the Illini Union, take the 50E Green to Lincoln Square garage east. From there, you'll need to transfer (overall unsure if it stays the same bus) to the 70. That will take you directly to Main& Brady. This ride is around 35 minutes. From there it is an approximate 4 min walk. This runs every 30 minutes, from  ~9AM-~5PM