StuartG said:
Trolleybuses have so many advantages over trams. Starting with the much lower infrastructure costs since they only have to add the overhead cable. All the other infrastucture is shared. No changes at road level are necessary. I believe the buses are cheaper and simpler than diesel so displacing diesel buses is easy.
Yes, this is a huge cost saving. Not only do trams require the installation of expensive track into the road surface, but services below the tracks need to be diverted out of the way, which I believe often costs more than the cost of laying the track.
Rubber tyres mean little sound - not the earsplitting metal on metal screeching on tight curves of trams. And no tram tracks to get caught in. Financially new trams (cf Croydon/Nottingham) have been generally regarded as disasters. Even the construction phase is traumatic.
Rubber tyres aren't as energy efficient of course, and tracks restrict the vehicle to a much narrower corridor so it can be easier to accommodate trams into pedestrianised areas for example, or to find space for segregated routes on verges, central reservations, disused railways etc. And there is the potential for conversion of heavy rail routes, or shared-use tram-train running, which can't be done with buses. I wouldn't agree that existing systems are regarded as financially disastrous- Nottingham's system has been very successful and they are going to extend the network; likewise Manchester.
Trolleybuses offer a much better passenger experience than diesel buses. Quieter, faster, vibration free. They give no on-street pollution and the CO2 emissions are much lower in electricity production than diesel burning. The disadvantages are the difficulty of temporary re-routeing in case of road works (doesn't seem to have been a problem 50 years ago!) and the complexity of interchanges of multiple routes. Which is why you may never see them again in central London but appear to be the public transport of choice in many smaller european cities today.
Well, as ever the short-sightedness of 1960s Britain is so apparent here, isn't it; and sadly the current approach to transport policy still insists that the rest of Europe (and indeed parts of the US) is wrong and that investing in good public transport is poor value for money...
One interesting development that is becoming apparent is the technological convergence between different public transport modes: diesel buses are starting to incorporate hybrid technology which offers many of the benefits of the trolleybus, while trolleybuses are starting to use back-up power sources so they can run of the wires like conventional buses. And for all types of bus there are bus priority and guided-bus technologies, helping them to avoid traffic congestion and so provide an advantage over car travel. There's even the bus that runs on rails...
http://www.wired.com/autopia/2008/05/half-bus-half-t/