I have lots of friend who are police officer they go on about this all the time! and say it drives them mad.
All they ask for is that cars, trams, buses just stop best they can.
They find that cars wont stop or when vehicle stop for them other cars over take them!how dangerous!! is that!.
The thing with the trams is that they will stop and then its for the police officers to wait for a space and ensure its safe before going!
It hard sometimes if say there is 2 cars travelling 2 an incident.
There is no guidence on this however most people last year got some leaflet through the post telling you what to do. Not sure where ya would find this tho