Some ideas for my own ALT history
By 1951, the President Eisenhower pass on Congress the American Transport Act, to upgrade and modernize american transportation infrasctructure and a way coordinate the postwar growth of the road, rail and air transportation system and create a multimodal system. The Act make the creation of a more trunk higway system and local road developements, new higher speed mainlines without railroad crossings and speed service, electrification projects and upgrade of existing main routes, network of regional air and airships terminals for the national transportation network on major cities, upgrade of interurbans to rapid transit subways as way to attend the new boom population and suburbs or creation of entire new metro systems and expand the exists one.
In 1953, works begin in upgrade the entire northeastern corridor and the built of the newly-four track Hudson Tunnels and Boston North-South link and a way to permit double-deck trainsets as electrification of entire corridor. Together if this, all sinalization and tracks are now permited to 210 kph speeds. This is all make for creation of the first super express american trainset, the “Superliner” by Pennsylvania Railroad, that enter in operation in 1956.
On Rapid transit, during all 50s and 60s, the cities of New York, Boston and Chicago upgrade they "old style" subways and expand in much way, and built of new rapid transit systems begin on D.C., Cincinnati, Detroit, Atlanta, Denver, Seattle, San Francisco and Miami. Los Angeles upgrade they massive interurban Pacific Electric system to a rapid transit lines and use of new streamliners EMU built by St. Louis Car Company and Budd.
Construction together of Interstate Trunk Highways are the new "Mainlines" railroads, link the main cities and industrial areas, entire electrificated, and if transporation hubs on newly-built Airports as LAX, Chicago O´Hare and New York City, if Union Stations inside of these. To operate these high speed lines if 200 kph, the American Government and Railroads create in 1961 the Amtrak, focus to operate this new high speed and intercity services. Train models as the XG-100 built by ALCO/Budd and the Superliner-II double-deck built by GE became the common model on these routes. Some trains even have coaches that permit transport cars and trucks on them.
Traditional mainlines are upgrade and focus more on freight service, and much of these lines in both cases became electrificated as New York Central, Baltimore & Ohio, P.R.R., Southern, Illinois Central, D&RGW, Milwaukee Road and Southern Pacific. This occur thanks to cheap energy provide by newly nuclear power plants built during the 60s. Common models became the GE E-44, EPH-60, EF-4, E5AC and E60 and EP-70 during late 50s up 60s.
New York City subway pass to a massive upgrade during the 1958 - 1964, know as "Program for Action", that built more than 80 miles of new tracks, rebuilt of mostly old stations and renewal of entire fleet by new trainsets made by Budd and GE, as well improve and modernize the Brooklin streetcars service. (ALT, NYC Subway as well mostly of rapid transit never came to a shutdown and gritty image and graffitti never occurs). In 1975, works begin on Phase I of New York Express Rail, similar to BART of San Francisco, these system would be link JFK, Manhattan if a stop on second level of Pennsylvania Station (never-demolished) and New Jersey.
By 1964 up 1980, railroad traditional passenger service view a massive decline, but the Amtrak Superliners and the Streamliners trains from roads as Union Pacific or PRR still continue to see a great use, for both intercity of a luxury-cruise by the tracks. Introduce in 1968, the Auto-Train became a common thing as people could be ride on luxury trainsets and use they cars during holidays or coast-to-coast.
In 1968, after the merger of ACL and Southern in Atlantic Southern, they became the first road to introduce Turbotrains on US, inspired on services that begin occur in France and Germany at that period. Routes from Miami to NYC and New Orleans became common use of them, and later expand to be used on dense areas of Pennsylvania Pacific.
By 1972, the Oil Crisis made streetcars make a comeback, in form of newly light-rail lines. American medium and large cities have a integrated transportation system that use streetcars, commuter rail, subway, high speed rail and buses for low denses areas up railroads terminals.
Would be add another ideas later.