When approaching a stationary vehicle with a red beacon, everyone stops and continues only with permission. Public transport vehicles are no exception, and simply slowing down is not enough.
Under the traffic rules, when approaching a stationary vehicle with a red flashing beacon switched on, all drivers traveling in that direction are required to stop (clause 31). They may continue only after receiving permission, and public transport (route) vehicles are no exception.
Option 2. Just slowing down is enough when approaching a stationary vehicle with a blue, or blue and red, beacon; at a red beacon you must stop.
Option 3. Public transport vehicles have no exemption from the mandatory requirement to stop when there is a red beacon.