What was one effect of the interstate highway act of 1957?
the emergence of the car as america’s main mode of transportation
the creation of speed limits as a result of increased highway accidents
the sluggish development of the airplane industry
an increase in the populations of midwestern and western cities
fewer jobs because the railroads lost business

an increase in the populations of midwestern and western cities

Explanation:

The construction of the Interstate Highway Network was authorized by the Federal Aid Highway Act of 1956, popularly known as the Interstate and Defense Highways Act of 1956.

It was a petition of the largest automobile manufacturers in the United States and promoted by President Dwight D. Eisenhower - influenced by his experiences as a young soldier crossing the United States in 1919 following the route of the Lincoln Highway and the knowledge of the motorway network German (Autobahnen) during World War II - as a necessary component of a national defense system. This would make possible a better displacement by land of troops and military supplies.