Most diseases, including COVID-19, are spread by inhaling droplets of respiratory tract fluids (coughs, sneezes, saliva while speaking), not through contaminated surfaces. So while a great idea and of some value, UV treatment won't solve the problem of the risks of closely packed buses and subway cars. Masks, face shields, or even expensive power assisted personal respirators (PAPRs) are a more practical, but less acceptable to most people intervention. Herd immunity, vaccines and anti-viral drugs are the other part of the equation, but these take time for a new virus.
Until some of these issues are resolved, public transit will remain more dangerous and less used than in the past. We've learned a lot from this pandemic, and some of what we have learned is that getting human beings close together in large numbers has risks.
