Page:America's Highways 1776–1976.djvu/448

 * The flaw could not have been detected by any inspection method known to the state-of-the-art today without disassembly of the eyebar.

These revelations led to a program of immediate bridge inspections and bridge inventories directed by a committtee formed at the direction of the President. As a result of this committee’s actions, new inspection equipment is being developed and purchased and sophisticated devices are being employed for inspecting bridge members and for determining scour at bridge piers. Bridges deemed unsafe are being closed to traffic, and bridges are being reappraised as to load capacities.

The 1968 Federal-Aid Highway Act mandated national bridge inspection standards for the Federal-aid systems. These standards establish inspection qualifications and require biennial inspections. All States are required to maintain written inspection reports and a current inventory of all bridges on the Federal-aid systems.

The 1968 Act also required that an inspector training program for employees of the Federal and State governments be established and be kept current with new and improved techniques. In the Federal-Aid Highway Act of 1970, a bridge replacement program was required to replace substandard bridges over waterways and topographic barriers. This program is now in full swing. Many of the most deficient bridges have been or are being replaced. There are thousands of bridges on the Federal-aid system that are posted as having limited capability of carrying truck traffic. It is presently estimated that replacement cost would be approximately $2.3 billion.

The 60 years since the first Federal-aid act have been a challenge to the bridge engineer. The first goal was to set a plan of cooperation and encouragement between Federal and State organizations in developing bridge standards, then to devise a comprehensive and workable program for planning, designing, approving and inspecting Federal-aid bridges to meet the current and predictable future needs of traffic. With no early background for predicting traffic growth and facing an unprecedented increase in vehicle volumes, speed and weight, increased higher standards for width, alinement and strength of bridges were required, and many existing bridges became obsolete.

Continuous and careful attention to new developments was necessary to maintain current criteria and specifications for bridge planning and design. The first 60 years’ pursuits and accomplishments leave a background of experience and knowledge for continued accomplishmment of future comprehensive programs.

As was the case in Europe, tunneling activity in this country began with the mining industry, followed by canal tunnel construction, then the railroads and finally highways. Most of the early canal and railroad tunnel work was done in Pennsylvania, but California holds several important “firsts” for highway tunnels.

By stretching the definition of a highway tunnel to include tunnels constructed for horsedrawn traffic before the automobile came into general use, probably the oldest highway tunnel in the United States is located in California. Built during the 1870’s, the tunnel pierces a high rock cliff on the Pacific Ocean about 6 miles south of San Francisco. Complete and accurate records concerning this tunnel are lacking, but historians speculate that the bore was built to permit local ranchers easy access to San Francisco along the beaches.

The first tunnel of substantial length constructed to accommodate automobile traffic is also located in California. Completed in 1901, the Third Street Tunnel passes through Bunker Hill in downtown Los Angeles. Interestingly, the contractor made an unsuccessful attempt to use a tunnel boring machine on the project.

The pioneer spirit and Yankee ingenuity of American tunnel builders was perhaps most evident in the 1920’s. During this era, some of the most famous highway tunnels in the United States were built. Early in the 1920’s a comprehensive research program developed the fundamental data for vehicular tunnel ventilation. The research was conducted in connection with the design of the Holland Tunnel. Passing under the Hudson River between New Jersey and New York, the Holland Tunnel was the first major subaqueous vehicular tunnel in the United States. It was opened to traffic in 1927. Three years earlier the Liberty Tunnels were completed in Pittsburgh, Pennsylvania, and, at 5,800 feet, were the longest highway tunnels in the country at that time. About the same time, the Posey Tube under the estuary between Oakland and Alameda, California, was nearing completion. When opened to traffic in 1928, the Posey Tube became the first highway tunnel in the world to be built by the “trench method.” An American innovation, the trench method consists of sinking pre-fabricated tunnel sections into a prepared trench on the riverbed. A total of 13 highway tunnels have been built by the trench method, the latest being the Wallace Tunnel on Interstate 10 in Mobile, Alabama, opened to traffic in 1973.

The decade of the 1930’s saw most of the tunnel construction being concentrated in the western States. Many of these tunnels were located on the new access routes into the national parks. Probably the most notable accomplishment during the 1930’s was the Yerba Buena Island Tunnel connecting the San Francisco-Oakland Bay Bridges in California. Completed in 1937, it remains the only double-deck highway tunnel in the country.

Immediately following World War II, tunnel construction activity quickened, and in 1950 another record was established. The Brooklyn-Battery Tunnel under the East River in New York City became the longest highway tunnel in the country—a distinction it still holds today.

Since the early 1960’s, the bulk of U.S. highway tunnel construction has been within the Interstate System. To date 15 major tunnels have been completed on the Interstate, 4 are under construction and 13 others are under design. These facilities are designed to safely handle high-speed traffic, a far cry from that narrow passage carved through a cliff on a California beach. 442