Question

what is the least common mode of transportation in the united states?
water
road
air
pipeline

Explanation:

In the United States, road transportation is extremely common for daily commuting and freight (e.g., trucks on highways). Air transportation is used for long - distance travel (both passengers and some high - value freight). Pipeline is used for transporting oil, gas, etc., especially across long distances. Water transportation (e.g., ships for international trade and some domestic freight along waterways) is less common compared to the other three in terms of overall usage frequency for general transportation needs (excluding specific industries like international shipping which is important but still has a more limited scope in the context of all transportation modes in the US).

Answer:

water