On Fri, 06 Mar 2009 19:15:08 +0700, Bruce In Bangkok
wrote:

I suspect that just as an engineer wants to
design the best bridge

Normally they design the minimum, that is cheapest, that will do the
job. This does not mean no safety margin. There is, however, no point
to making the deck far stronger than the piers. As for the best,
nobody wants to pay for it. They want good enough, and as cheap as
possible.

Casady