Final answer:
The passage of the Interstate Highway Act of 1956 led to a drastic improvement in the ability to travel across the nation by automobile.
Step-by-step explanation:
One of the main effects of the passage of the Interstate Highway Act of 1956 was the drastic improvement in the ability to travel across the nation by automobile. The construction of the federal interstate system and its 40,000 miles of highways facilitated private and commercial transportation, making it easier for people to travel long distances by car. This led to an increase in road trips, tourism, and the mobility of goods and services.