Louis T. Klauder and Associates (LTK) is a professional rail transportation engineering consulting firm. It was established in Philadelphia in 1921 by Louis Tobias Klauder (1880-1945), a former construction engineer for the Philadelphia Rapid Transit Company. After Louis Tobias Klauder’s death in 1945, the firm was converted from a full proprietorship to a partnership with his son Louis Thornton Klauder (1908-1999) as managing partner. Under his leadership, the firm became internationally known for its consulting work on rail and transit projects.

In 1964, Japan introduced it’s first "bullet trains," the New Tokaido Line between Tokyo and Osaka. This prompted an initiative to improve ground transportation in the northeast United States. In September 1965, President Johnson signed the High-Speed Ground Transportation Research and Development Act, which facilitated the development of a high-speed rail corridor from New York to Washington along the existing Northeast Corridor right-of-way. The project was called the Northeast Corridor Demonstration Project and was a joint venture between the United States Department of Transportation and the Pennsylvania Railroad. This program was active between 1966 and 1972, and marked the entry of the U. S. into the era of modern, high-speed rail passenger transportation.

LTK was hired as consulting engineers to prepare estimates, develop specifications, secure bids from contractors, and then oversee implementation of the project as intermediaries between the participating companies (the railroads and equipment manufacturers) and the government administrators. Klauder also helped the U.S. Department of Transportation develop the High Speed Ground Test Center's test track near Pueblo, Colo., on which a variety of rail or tracked vehicles could be tested.

A large portion of the Northeast Corridor was originally built between 1830 and 1917 by two different railroad companies: the Pennsylvania Railroad and the New York, New Haven and Hartford Railroad. The New Haven line was not electrified east of New Haven and had many curves as it wound along the Long Island Sound. LTK was to determine how to straighten or relocate parts of the line in order for the trains to reach the desired speed.

Longtime rival companies, the Pennsylvania Railroad and the New York Central Railroad announced merger plans in November 1957. The merger was approved by stockholders on May 8, 1962, however, the Interstate Commerce Commission (ICC) did not approve the merger until four years later. The merged company officially began on February 1, 1968, as the Penn Central (PC) Railroad. Penn Central was required to absorb the New Haven line in 1969 as a condition of the merger, which brought the entire Washington-Boston corridor under the control of a single company. Penn Central declared bankruptcy on June 21, 1970. Amtrak began operations on May 1, 1971.

During this time of railroad mergers and bankruptcies, a product of the Northeast Corridor Demonstration project was a high-speed train called the Metroliner. After several years of development and prototypes, the Metroliner entered service in 1969, but due to the unreliability of the trains and several technical problems it wanned in usage in the 1980s and did not become the high-speed train solution that it was intended to be. Throughout the 1960s, 1970s and 1980s there were numerous planning studies and government sponsored projects intended to improve railroad transportation.

LTK's involvement in the Northeast Corridor tapered off during the 1980s. Louis T. Klauder and Associates is still a partnership; in 1994 it began doing business under the name of LTK Engineering Services. The firm has relocated its headquarters from Center City Philadelphia to suburban Ambler and maintains several branch officers around the country.