Is the highlighted past conditional in this sentence the right verbal tense?
The cycling path was in fact made on the route of a dismissed railway that in the golden age of rail transport ran up the two main Bergamask valleys. Inaugurated in the first decade of the 1900ís, it was later abandoned for road service in the 1960ís, to the bitter regret of present-day public administrators who have come round to the fact that with levels of road traffic worryingly high the little train would have made a useful asset.
from my blog
The tense is right, but I prefer '. . .would have been a useful asset.'
Incidentally, it's a disused railway, not a dismissed one.
And is this right:
We left the kitten on the balcony at night and the next day we found that a bigger cat had climbed up to the second storey attracted by the miaowing. We were so surprised! We wondered how a cat could have climbed a smooth wall like that.
Or do I have to say "could climb"?
I'd say the cat could have climbed and maybe use something like sheer instead of smooth.
While I was brushing my teeth earlier I had an inspiration and thought that it was "was able to climb" that corresponds to my meaning.
I expect "could have climbed", which Tdol accepts as a viable option, refers to the ability in general, whereas "was able to climb" refers to the actual feat of doing it on the specific occasion.
Is it so?
Yes, was able to is fine.