Answer :

The Transcontinental railroad greatly affected US commerce in the sense that it made the transportation of goods far easier and cheaper, which reduced prices.
Greenleafable
It boosted the economy drastically and the wealth skyrocketed. It was made possible to transport goods all across the United States which reduced the prices and made goods readily available fore everyone which opened new markets and also made companies stronger. With stronger companies they paid more taxes so the government also experienced prosperity.