Which Transportation development has the greatest long-term impact on the American economy

Steamboat

Canal system

Horse-drawn cart

Steam locomotive

steam locomotive was the fastest mode of transportation. therefore it also was spread the fastest. In half a century it spread to almost all of US.

Explanation:

steam boats and canal system transportation were slow moving. the idea of a flat rail road was derived by horse drawn carts. All in all, without a doubt, steam locomotive has had the greatest long term impact on American economy (even if several inventions and improvisations had to be made through).