In the Cache Valley Region, Utah, all buses are free.
This is why they have free public transport according to the Cache Valley Transit District:
If any fare were added, a significant amount of time would need to be added to the current schedule to accommodate people depositing fares. The addition of a fare reduces CVTD’s ability to provide convenient and timely service.
 Maintain Ridership
Research conducted by independent transportation consultants indicate that CVTD’s ridership could drop considerably if fares were added. If ridership dropped it could place hundreds of vehicles on our already congested roads.
 Alleviate Fear
There are various reason people may be uncomfortable with riding the bus—getting lost, riding with people they do not know or missing the bus. The addition of fare would add to the list, causing more questions like "what is the fare," "do I need exact change," or "what if I don’t have cash?" Being fare-free keeps it simple and increases ridership.
 Keep Operating Costs Low
The cost to install infrastructure for fares would be between $400,000 and $500,000. Significant additional ongoing costs would be incurred such as fare box maintenance, counting of fares, training and collection of fares by an armored car service.