[feoren]

> you can copy software rather easily, but you cannot copy a bridge

You can copy a bridge just as easily as you can copy software: just print another copy of the blueprints. Just change the header from the name of one project to another, and you're done with the engineering at that new site. What's that, the span length is different? The soil is different? The traffic patterns and weather patterns and political climate and regulations are different? Of course they are. And when you copy source code, the use case is different, the hardware is different, the database is different, the inputs are different, the client is different. Every engineering job is custom. Software and bridge. The two disciplines are not as different as you say.

Bridge engineering also undergoes an "agile" methodology as the plans are repeatedly changed during conversations with the client, discovery of new regulations, ground-truthing, etc. Remember: the outcome of engineering is plans, not a finished product.

You're talking about differences in constructing the thing, after the engineering is complete. That's largely irrelevant to the engineering cost.

[valenterry]

Now you have copied the blueprint, but not the bridge. (and before you complain that software is also just a blueprint, the difference is: in one case you estimate the blueprint and not its execution, in the other case both (or even just the execution)