Dogs on buses

When did it happen that you couldn't bring dogs on Dublin buses? Apparently it's "at the discretion of the driver", but drivers are resolutely-anti-pooch, except for a grudging okay to guide dogs.
It certainly wasn't the case in the 1920s, when my mother and her brother and their dog Bran toured the city on trams - unwillingly in the case of Barbara and Don. Bran was an Irish terrier with a mind of his own, and if he saw the No 19 tram passing by, he would set off, the two small children towed behind him, and get on and go upstairs using the stairs at the back. (Dogs were always allowed, but had to be brought upstairs, the same as cigarettes, in those days.) Upstairs, then, often meant in the open air, and Bran didn't mind if it was raining.
When Bran felt like getting off, off he'd get, the two children gripping the lead behind him as he went down the second set of stairs at the front of the tram.
On the way home, Bran might take a vagary to have a walk in the Green Fields, beautiful drumlins now long lost, which were accessed by way of the Dark Lane, a winding, lovely lane overarched by the branches of the trees that lined it, now subsumed into Sundrive Road.
In the 1950s and 1960s and 1970s there were always dogs upstairs, on their way to their walk in the park. When did this end? Perhaps when conductors were ousted and Dublin's buses became driver-only? Or when cars started to be a thing everyone had?
You can blame the no-dogs rule for a certain amount of climate change; how many car journeys would be saved (and how much income added to the public transport purse) if dogs could take their place on the top deck again?

 Lucille Redmond's ebook, Love, gripping dark and funny stories of love and revolution, is available on Amazon and iTunes