Which commission regulated markets that trucks could serve under the Motor Carrier Act of 1935?

The Interstate Commerce Commission (ICC) is the correct choice because it was established to regulate railroads and later expanded to include trucks and other forms of transportation. Under the Motor Carrier Act of 1935, the ICC was given the authority to regulate interstate trucking operations, including the markets that motor carriers could serve. This regulation aimed to ensure fair competition, set appropriate rates, and protect the interests of the public and carriers alike.

The other organizations listed have distinct roles. The Federal Maritime Commission mainly oversees maritime commerce, the Department of Transportation governs all transportation modes and policies but does not specifically focus on trucking regulation like the ICC did, and the National Highway Traffic Safety Administration is dedicated to road safety and vehicle standards rather than the regulatory aspects of trucking services.