utility until the pressures of continued traffic growth necessitated reconstruction during the 1960’s. Much of this beauty was retained in the reconstruction process.
The example set by the Bronx River Parkway and other early controlled access highways went largely unnoticed for many years, mainly because one of the primary functions of highways at that time was to serve the abutting property, not to isolate the road user.
During the period 1930–1940, highway designers became aware of the adverse effect that unregulated access could have upon highway traffic service. Strip commercial development in the vicinity of towns and cities was particularly troublesome, Vehicles turning into and out of roadside businesses created congestion and caused accidents. A few far-sighted individuals recognized the principle of control of access that had been pretty much dormant throughout the 1920’s. Interest was not limited to the United States. In 1933, the first spade of earth was turned on a new system of highways for the German Reich. These autobahnen, with full control of access and designed for speeds up to 120 miles per hour, were destined to exert considerable influence on American design criteria.
The roadbuilders in the United States demonstrated, however, that they were not dependent on the German engineers for leadership in designing and constructing freeways. Between 1934 and 1940 the Merritt Parkway was constructed, extending the parkway and controlled access features of the Westchester County, New York, parkway system across Connecticut. During its first full year of operation, it handled an average of 20,000 cars per day.
The Merritt Parkway near Darien, Conn.
The need for a traffic artery capable of handling similar traffic volumes between Los Angeles and Pasadena led to the start of the six-lane Arroyo Seca Freeway in 1938. It had two 35-foot roadways with a 6-foot curbed median.
The Pennsylvania Turnpike, completed in 1940 from Irwin to Carlisle as a toll facility, was the first rural freeway of notable length in this country. It was a four-lane divided highway, except for several tunnels through mountains where the width was narrowed to two lanes. Noteworthy features in the design standards were gentle alinement and relatively flat gradients suitable for high-speed travel despite the ragged terrain traversed by portions of the route. Also, consistent with anticipated high-speed travel was a design requirement for speed change lanes 1,200 feet long at points of access.
These and the several other freeways in use by 1940 met with immediate acceptance by the motoring public. The freeway era was born.
The Era of the Freeway: 1940–1976
Design Standards
Concentrated thought and effort toward a nationwide system of controlled access highways, both urban and rural, began to gather momentum about 1940. However, it would be totally erroneous to leave the impression that no further advances were made in the design of conventional highways after that date. It is generally true that the advances were in the nature of refinements of the basic concepts and principles enunciated in AASHO’s seven published design policies. These refinements generally took the form of more generous dimensions in such elements as pave-
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