Stewart,
I think this exemption is basically to allow us to do our job. We don't normally hold our radios in the hand anyway, they are generally clipped to our jacket and car sets have PTT buttons mounted on stalks next to the steering wheel. The same offence of Fail to maintain proper control or Careless driving will apply to anybody committing those offences. Not sure if many people apart from truck drivers still use 2 way radio.
