Vancouver has three rapid transit lines, two of which have underground segments, that cover on the order of 70 kilometres. Most people here think that the city is underserved by rapid transit, and I agree - they should also build the Evergreen line and an extension along Broadway to UBC.
There is nothing even remotely analogous to this kind of investment in Halifax, nor is there the same spirit of seriously tackling the problem of building proper infrastructure and exploring the introduction of novel technology.
I find the "big city transit" argument really tiresome, along with its not-yet-dead ancestor, reverse Maritime exceptionalism (no matter how things actually look, they must be worse than everywhere else!). Having lived in Vancouver and Toronto and having been to places like New York and Los Angeles I am aware of the fact that Halifax is not a large metropolis, but people there are too quick to reject the experiences of other cities.
Instead of offhandedly rejecting elevated trains (and, let's remember, the city's not even there - they reject
all rail transit), it makes a lot more sense to look at the actual costs vs benefits. The infrastructure is more expensive, for example, but it can be easily automated so that drivers and not needed and so that it is feasible to run smaller trains. This is very significant for a line that will exist for 50-100 years, and in Halifax it's the kind of thing people never even think about because it's supposedly too rich for the city's blood or whatever.
I don't think that Halifax will stop growing before it hits 500,000 people. The last StatCan estimate was that it added something like 6,000 people in 2008, making it one of the faster growing cities in Canada, probably comparable to Vancouver. Again, the attitude that the bottom is always about to fall out is poorly supported exceptionalism. A more reasonable explanation is that growth will more or less continue as it has for the past 250 years or so, and that if nothing is done now then the city's infrastructure will be lacking in 15-20 years. Of course, if the good old Maritime attitude holds then people at that point will tell themselves that that's to be expected there and that the city's about to stop growing at any moment anyway - why build transit in a little town of 500,000 that will never hit 750,000?