This is a fantastic site about the relative merits/demerits of trolley buses, it also has some great mockups of pictures of trolley buses in Edinburgh: www.scottishelectrictransit.org.uk although none of them going around roundabouts or stuck across a set of traffic lights. (The picture in the link is of a trolleybus at Elm Row, though the artist’s impression does not show there being six other buses there at the same time, which is normally the case).
Don’t get me wrong, I have nothing against trolley buses, and if trams are ever ruled out I would start campaigning to have trolley buses instead as the next best thing. In fact, once we get trams, we could then start campaigning to have trolley buses put in around the rest of the city.
The main argument against trolley buses is that to get near the same benefits as a tram, you would need to segregate them from the rest of the traffic on separate routes, especially if you want one trolley bus to carry as many people as a tram. That would involve almost as much work as installing a tram line. Those who think that trolley buses are a quick, simple alternative to trams really need to look into the matter a bit more closely.
The way to think about it is to think of a bendy bus. That was trialled in Edinburgh and quickly withdrawn. To make it work would need drastic changes to the infrastructure and layout along the whole route, such as junctions, traffic lights, roundabouts etc. That can be done, by the way, with similar (but not quite as much) disruption as trams, but for a little extra money, you may as well have trams.
Click on this link and see a picture of a 200 person trolley bus in Geneva and imagine it going round the roundabouts at the top of Leith Walk. (By the way, Geneva is busy replacing its buses with trams – see the link to the right about trams in Switzerland).