I don't think you read what I wrote. Of course engineers need to understand all the requirements for the bridge. But coming up with those requirements, ie des

I don't think you read what I wrote. Of course engineers need to understand all the requirements for the bridge. But coming up with those requirements, ie designing the economic/business case, is a separate discipline. As someone said, some of that may also be engineering; economic engineering, traffic engineering, social, political etc, but it is not bridge engineering.