Final answer:
The highway type known as a trunk line is the Expressway, which is a controlled-access highway that forms part of the Interstate Highway System, influenced by the German Autobahn and central to urban connectivity.
Step-by-step explanation:
The highway type also known as a trunk line is typically referred to as an Expressway. This classification of highway is designed for high-speed vehicular traffic, with controlled access, and is an essential part of the larger Interstate Highway System. Beginning in the 1950s, the growth of car ownership led to the expansion of local and state roads, culminating in the formation of the Interstate Highway System. This vast network was heavily influenced by the German Autobahn, which impressed President Eisenhower due to its efficiency and the role it played during World War II. As a result, the Federal Aid Highway Act was passed in 1956, which allocated funds to construct these highways, fundamentally changing the urban landscape by enhancing connectivity between cities and suburbs.