Over here there aren't any such screens, the driver is not enclosed in any way from the rest of the bus
Ye gods, on some of the routes we ran, the driver would have no chance in a bus like that..! I remember an incident that happened to a colleague not long after I'd started with the company. He was driving the last bus of the night, and it stopped short of the usual terminus by around 5 miles or so, which was the closest point to the depot.
He'd arrived at the point where he finished service, and there were still three passengers on the bus, at the back. He turned to them and told them, politely, that he was now finished for the night and they would have to get off. Remember that this bus clearly stated on the destination blind at the front that it finished short of its usual terminus, and he would have informed all passengers getting on of this as well, in case they hadn't seen the blind.
The three guys at the back, who were all very rowdy and probably drunk into the bargain, came to the cab and said "We want to go to XXXXXXXXX" (being a point a couple of miles further down the normal route). The driver told them, again very politely, that he could not go any further as he was now out of service. The response was again, "We want to go to XXXXXXXXX". Again he told them he was finished for the day.
Whereupon they wrenched the cab door open, dragged him out, and beat him senseless, breaking three of his ribs into the bargain. He was off work for several months, in fact he never did return, and the last I heard had not worked again. By the way, he was a very well built man, who could normally take care of himself, but against these guys he had no chance.
I should emphasise that this incident was a rare one, I don't want to give the impression drivers got beaten up every day, but it indicates the sort of thing that can happen in certain areas if the driver has no protection from some elements of society.
This was, by the way, before the days when all the buses were equipped with CCTV, so there was no evidence to be able to identify the offenders. It was one of the reasons I decided to move from driving to a job dealing with the onboard CCTV systems.