Yes, the government practiced laissez-faire economics when promoting railroad construction.
This is because laissez-faire economics is a type of economics that is determined solely by the power of demand and supply without the intervention of the government.
Laissez-faire economics is considered to be a total or pure capitalism where the only influence is the force of demand and supply.
Since the railroad construction in the United States in the 19th century was built by the private sector or individuals, and the prices of transportation were determined by the market forces,
hence, in this case, the correct answer is "Yes, the government practiced laissez-faire economics when promoting railroad construction."
After the war, the Treaty of Paris was signed, which also stopped the war, and Britain got just about all of the American property France had owned, if that's what you're referring to.
