Originally Posted by cyccommute

The current price per mile in the US that I can find is about $150,000 to $200,000 per mile for a 5 foot path. That's half the width of a "normal" bike path so $300,000 to $400,000 per mile. Add in a bridge and that will cost $400,000 to $1,000,000 depending on the length. A 3000 mile "bicycle interstate" without bridges would cost around $900,000,000. Add in roughly 1000 bridges and the cost balloons to $1.9 billion.

It'll never happen...at least not in the US.