Well, if you want to use electric buses on a dedicated right of way, once you build all the roadway, cables (if you're talking trolleybus), level floor boarding stations etc, you're really not short of the infrastructure required to build a tram network. But really, when you're talking about infrastructure designed to be there for at least a century, I think you can discount the embodied energy argument.
I'm not meaning that though - I'm talking about the fact that we can now build electrically run buses that do not require on-road infrastructure.
The technology is there, and improving all the time. The costs are a fraction of that of trams, or indeed trolley buses. That means that the scheme can be rolled out over a wider distance.
Think about what we're specifically talking about here: One line, from the centre to the SECC. That needs its own dedicated type of vehicle! Shockingly wasteful imo. And when we talk about a possible roll-out elsewhere, then we really get into the big money. For less cost, you could re-nationalise the entire Strathclyde bus ownership, and use clean, modern buses.
That's before we even touch on the other differences:
The buses are more flexible. If one breaks down, it breaks down; traffic can go around it, and it doesn't block the bus route. This doesn't happen with trams.
The routes can be altered in instances of roadworks, or other accidents, or parades, or festivals, or whatever.
The same fleet of vehicles can be used for the entire network; that's not the case with trams. Trams can only be used on the very busiest routes of a transport network, where the vast installation costs will be at least partly offset by the projected usage. Thay can also only be used either on wide roads that can afford the loss of a lane in either direction, or on narrow roads that we can afford to turn over wholly.
And this infrastructure will not last a century! If it did, it's be near unique. Every time bits of it need replaced, it's adding to the energy consumption that could be avoided, and I sudder to think of the ancilliary knock-on effects in the meantime, such as the amount of pollution and congestion Edinburgh has suffered during the roadworks there recently.
But there are real advantages to trams over buses. People who wouldn't use buses are more likely to use trams. This isn't just true for locals; think of last time you were on holiday in a city with a light rail network. I'll hazard a guess that you used the trams, and didn't use a bus unless you really needed to. Trams promote urban development in a way that other forms of transport just don't do (obviously something we'd like to promote along the Clyde.) And of course even a two car tramset has a much higher carrying capacity than any bus, which makes trams ideal for major high capacity corridors.
I've heard those arguments before, and while I agree with them partly, I'm yet to see any hard evidence supporting them. The holiday reference is probably true, but it's a bit of a red herring, as I'm likely to be visiting the most obvious and popular places in a given city; seeing the famous sights, etc. It doesn't really say anything in favour of the trams when it comes to local people making the less glamerous journeys across their city that we all have to do..
Basically my problem is this: I don't deny for a second that the buses we have are shit, and that the system is shit, but this is something that could actually be solved by running the bus system differently. We don't actually have to install a whole new, very expensive, mode of transport to address these failings.