The Wall Street Journal remembers how the canals and railroads were built - by the private sector seeking to serve needs from economic growth.
In all of these examples, building infrastructure was never the engine of growth, but rather a lagging indicator of growth that had already occurred in the private sector. And when the infrastructure was built, it was often best done privately, at least until the market grew so large as to demand a wider public role, as with the need for an interstate-highway system in the mid 1950s.
There is a lesson here for President Obama: Government "investment" in infrastructure is often wasteful and tends to support decaying or stagnant technologies. Let the entrepreneurs decide what infrastructure the country needs, and most of the time they will build it themselves.