The transportation revolution was a time in American history when transportation within the country came to be much easier and cheaper. This was very important to the development of the US economy.
Before the transportation revolution, goods could only be transported (in places outside of coastal areas) by wagon or downstream on rivers. This made transportation in many places very expensive. With the transportation revolution, all that changed. First, there was the construction of canals that allowed two-way water transport and which connected places that had previously not been connected. Then there were steamboats that could carry relatively large loads upstream quickly. Finally came the railroads that did not have to follow waterways. All of these changes (which constitute the transportation revolution) improved the American economy.