Re: "2 bridges was 'unnecessary' says dev platform VP"
"As written, it's clearly a plural ("2 bridges") followed by a 'was'. It could have been written "Having two bridges was unnecessary"; but it was truncated into incorrectness. "The idea" (offered as a counter-example) is singular. Thus perfectly non-applicable"
The very nature of the article is that of the two approaches only one is really necessary. Therefore in the sentence "two bridges was unnecessary", we know that it's referring to the "idea" of two bridges, therefore it's singular. If the sentence had been "2 bridges were unnecessary", it would have implied that both bridges were unnecessary, and perhaps that there were actually more than two bridges.
Compare these two sentences:
"It was not necessary to have two bridges"
"Two bridges was not necessary"
If you think the second sentence ought to be "were", then reconsider when you see these two sentences, because that's effectively what you're saying:
"Two bridges were not necessary"
"It were not necessary to have two bridges"
In short, "two bridges was not necessary" is correct.