As you pointed out, there is a big difference between grandfathers who ferry their grandchildren to and from school and elderly taxi and PHV drivers. Another scary group are office workers who moonlight as PHV drivers in the evenings. I had the misfortune of being in a PHV driven by fatigued drivers in the early hours of the morning from the airport, on 2 occasions. Both explained that they were fatigued, owing to holding a day job and lacked sleep, but assured my family that they were able to control their cars.