Even just letting people know how full the bus is, in advance, would help a lot with that decision to take a cab etc. There could easily be a map or list of the physical buses and how full they are.
If the bus is full then the transit agency needs to run more service. Unless this is a "short bus" or your fares are unreasonably low (free fares are bad for this reason) your bus is paying for itself and you can run more service on that route to capture even more people.
NYC has this. Bus locations and estimated number of passengers on board: https://bustime.mta.info/m/index?q=M5