- The Early Years of the Pennsylvania Railroad -

• 1846, April 13, The Pennsylvania Railroad is chartered to build from Harrisburg to Pittsburgh and Erie
• 1849, The Pennsylvania Railroad enters an operating agreement with the Harrisburg, Portsmouth, Moutjoy & Lancaster, providing a connection to Philadelphia
• 1857, The Pennsylvania Railroad buys the Main Line of Public works
• 1860, John Edgar Thompson, Presendent of the Pennsylvania Railroad acquires a large block of the Northern Central Railway, and transferred ownership to the Pennsylvania Railroad, providing a link from Harrisburg to Baltimore
• 1861, The Pennsylvania Railroad leases the Harrisburg, Portsmouth, Moutjoy & Lancaster
• 1862, The Pennsylvania Railroad buys an interest in the Philadelphia & Erie Railroad
• 1863, The Leavenworth, Pawnee, and Western Railroad is reorganized as the Union Pacific Eastern Division (and later in 1869 as the Kansas Pacific Railway) as part of the Pacific Railway Act. The Pennsylvania Railroad invests in the railroad, and its effort to build a transcontinental railroad through Colorado
• 1864, With Pennsylvania Railroad aid, the Philadelphia & Erie connects Sunbury to Erie
• 1868, The Pennsylvania Railroad consolidates the Panhandle Railway and Stubenville & Indiana as the Pittsburgh, Cincinnati & St. Louis Railway
• 1969, The Central Pacific Railroad and Union Pacific Railroad meet at Promontory Point, Utah.  The Pennsylvania invests in both railroads
• 1869, The Pennsylvania Railroad leases the Pittsburgh, Fort Wayne, and Chicago Rail Road and the Columbus, Chicago & Indiana Railway
• 1869, The Pittsburgh, Cincinnati & St. Louis Railway leases the Little Miami Railroad, providing a line from Cincinnati to Dayton and Columbus
• 1870, The Kansas Pacific Railway reaches Denver, forming the first continuous transcontinental rail link across the United States (Union Pacific passengers and cargo must still cross the Mississippi River by boat)
• 1871, The Pennsylvania Railroad leases the Camden and Amboy, Philadelphia and Trenton, and Deleware and Raritan Canal Co., and United Canal and Railroad Companies of New Jersey
• 1871-1872, Thomas Scott serves as the president of the Union Pacific
• 1872, After buying the charter to the Baltimore and Potomac, the Pennsylvania constructs and opens a line from Baltimore to Washington DC
• 1873, Through service from Washington to Jersey City commences with a trackage agreement with the Philadelphia, Wilmington & Baltimore
• 1873, The Panic of 1873 allows Jay Gould to gain control of the Union Pacific Railroad.  The Pennsylvania Railroad sells its interest in the Union Pacific and is able to gain a controlling interest in the Kansas Pacific Railway.  The Pennsylvania Railroad also leases the St. Louis, Kansas City, and Northern Railroad           
• 1874, The Pennsylvania Railroad gains a controlling interest of the Allegheny Valley Railroad
• 1877, The Pennsylvania Railroad increases investment in the Texas and Pacific Railroad
• 1877, The Kansas Pacific Railway invests in the Denver, South Park and Pacific construction into the mountains of Colorado       
• 1880, Thomas Scott transfers his stake in the Texas and Pacific to the Pennsylvania Railroad
• 1881, The Pennsylvania Railroad leases the Philadelphia, Wilmington & Baltimore
• 1881, After reaching El Paso, Texas the Texas and Pacific is unable to continue west due to Southern Pacific expansion; the T&P enters receivership and is leased to the Pennsylvania Railroad
• 1882, The Pennsylvania Railroad connects to Mackinaw City, Michigan
• 1882-1884, Now under the control of the Union Pacific Railroad, The Denver, South Park and Pacific Railroad and the Colorado Central Railroad build branch lines toward Loveland Pass from both the east and west
• 1890, The Pittsburg, Cincinnati, and St. Louis and several other short lines are consolidated as the Pittsburgh, Cincinnati, Chicago, and St. Louis Railway

- Linking the Atlantic to the Pacific -

• 1898, The Pennsylvania Railroad and Kansas Pacific Railway provide financial and administrative assistance to the newly formed Colorado and Southern Railroad, which includes the former Colorado Central Railroad and Denver, South Park and Pacific Railroad, in return for a combined 20% stake in the new company. Combined with existing investments, the stake is enough to gain a controlling interest
• 1900, The Pennsylvania Railroad gains a majority ownership of the Northern Central Railway and leases the Allegheny Valley Railroad
• 1900, The Pennsylvania Railroad buys the Long Island Railroad
• 1901, David Moffat incorporates the Denver, Northwestern, and Pacific Railway and begins construction from Denver to Salt Lake City
• 1902, The Philadelphia, Wilmington & Baltimore and Baltimore and Potomac are consolidated as the Philadelphia, Baltimore & Washington, which forms the Washington Terminal Company with the Baltimore & Ohio to build a new Union Station in Washington D.C.
• 1903, The Western Pacific Railroad is incorporated by George Gould and Arthur Keddie to build from Salt Lake City, Utah to Oakland, California   
• 1904, The Pennsylvania Railroad begins construction of Pennsylvania Station in New York
• 1905, The Vandalia Railroad is incorporated to consolidate the lines west of Indianapolis
• 1907, Union Station Washington D.C. opens
• 1909, The Western Pacific Railroad opens for service between Salt Lake City and Oakland     
• 1910, Pennsylvania Station New York opens
• 1911, The Atchison, Topeka, and Santa Fe Railroad gains a controlling interest in the Denver, Northwestern, and Pacific Railway, which later connects to Salt Lake City, Utah   
• 1915, The Pennsylvania Railroad electrifies its line from Philadelphia to Paoli, PA
• 1916, The Pittsburgh, Cincinnati, Chicago, and St. Louis Railway, the Vandalia Railroad, and several short lines are consolidated as the Pittsburgh, Cincinnati, Chicago, and St. Louis Railroad
• 1916, The Kansas Pacific Railway leases the bankrupt St. Louis, Iron Mountain, and Southern Railroad
• 1917, The Penssylvania Railroad and Colorado and Southern Railroad jointly gain controlling interests in the bankrupt Denver and Rio Grande Western Railroad and Western Pacific Railroad      
• 1917, The New York Connecting Railroad opens in New York City, providing a link with the New York, New Haven & Hartford Railroad
• 1917, The Pennsylvania Railroad leases the Philadelphia, Baltimore & Washington
• 1918 - 1920 The assets of all United States railroads are held by the United States Railroad Administration during World War I
• 1920, Following three years of joint operations in Colorado, the need for a shorter route from Denver to the west has become clear. The Denver and Rio Grande Western Railroad converts track from Leadville, Colorado to Keystone, Colorado to standard gauge. The Colorado and Southern Railroad begins converting the Clear Creek Canyon route from Golden, Colorado to Bakerville, Colorado to standard guage and double track. The Pennsylvania Railroad surveys and begins construction of a double track tunnel from Bakerville, Colorado to the Montezuma mining district near Keystone, Colorado under Loveland Pass
• 1921, The Pennsylvania Railroad leases the Pittsburgh, Cincinnati, Chicago & St. Louis Railroad
• 1922, The Western Pacific completes a branch to San Jose, California, and the Tidewater and Southern Railroad, which is under Western Pacific control, extends to Fresno, California
• 1922, The Western Pacific buys the Sacramento Northern Railroad
• 1923, The Cassatt Tunnel under Loveland Pass is completed and operations begin over the new high line from Golden, Colorado to Leadville, Colorado
• 1924, After a year of operation, the high line is found to be inadequite due to the high altitude and heavy snow over Fremont Pass. A tunnel under Vail pass is surveyed and constuction begins.  Double track is extended from Keystone to Grand Junction, Colorado
• 1926, The Scott Tunnel is completed, and operations are shifted off of the high line
• 1927, the Pennsylvania Limited makes its innaugural run from Oakland, California to New York and Washington DC
• 1928, The Pennsylvania Railroad electrifies its line from Philadelphia to Wilmington, DE

- The Pennroad Corporation -

• 1929, The Pennroad Corporation is formed to hold the assets of the Pennsylvania Railroad and its subsidiaries
• 1930, The Pennroad Corporation reorganizes all of its holdings under three subsidiaries: the Pennsylvania Railroad, the Colorado and Southern Railroad, and the Western Pacific Railroad
• 1930, The entire mainline from Saint Louis, Missouri to Oakland, California is upgraded to at least double track
• 1932, Plans are finalized by the California Toll Bridge Authority for construction of the San Francisco-Oakland Bay Bridge. The structure is only designed to allow for lightrail operations on the Bridge Railroad on the lower deck. The Pennsilvania Railrod, Western Pacific Railroad, Sacramento Northen Railroad, Southern Pacific Railroad, and Santa Fe Railroad jointly form the San Francisco Union Railroad Company to build an electrified heavy rail connection under the bay. Each railroad takes an equal share of the new company, giving the Pennroad Corporation a majority stake
• 1933, The Pennsylvania Railroad electrifies its line from Philadelphia to New York
• 1934, The Pennroad Corporation secures PWA money to electrify many of its subsidiaries' mountainous lines in California, Colorado, Pennsylvania, and the entire Pennsylvania Railroad mainline from New York to Washington
• 1935, The Pennsylvania Railroad electrifies its line from Wilmington, DE to Washington, D.C. and Quantico, VA
• 1939, The San Francisco Union Railroad Company completes a link from the Southern Pacific Railroad's 3rd and Townsend Depot under the Transbay Terminal and under the San Francisco Bay to Oakland. Union Station San Francisco opens across Mission Street from the Transbay Terminal, and a new Western Pacific Headquarters building opens across Market Street from Union Station. The Transbay Terminal and Western Pacific Headquaters all have direct access to the Union Station platforms, with the REA offices housed in the ground floor of the Western Pacific Headquarters
• 1939, The Pennsylvania Railroad completes its PWA projects
• 1945, The Pennsylvania Railroad electrifies its lines on Long Island
• 1948, The Pennsylvania Railroad, Colorado and Southern Railroad, and Western Pacifc Railroad begin extending clearances on major passenger routes for dome cars
• 1949, The California Zephyr makes its innaugural run over the Western Pacific Railroad, Denver and Rio Grande Western Railroad, Colorado and Southern Railroad, and Chicago, Burlington, and Quincy Railroad, with connecting service east of Chicogo over the Pennsylvania Railraod
• 1950, The Pennsylvania Limited is upgraded with new Blue Ribbon Fleet cars.  The parlor car is a Superdome parlor and the observation car is dome parlor. The California Limited makes its innaugural run
• 1950, The Colorado and Southern advertises and operates the first "ski train" with service to Arapahoe Basin and Loveland Basin

- The Pennsylvania Railroad Corporation -

• 1950, The Pennroad Corporation consolidates all of its holdings east of St. Louis as the Pennsylvania Lines and reorganizes itself as the Pennsylvania Railroad Corporation
• 1952, The Pennsylvania Railroad petitions the BART commission in the San Francisco bay area to build and operate the BART commuter system with state and local subsidies
• 1957, San Francisco Bay Area voters approve the Pennsylvania Railroad proposed commuter system
• 1957, The Pennsylvania Railroad announces that its Pennsylvania Lines are in merger talks with the New York Central Railroad
• 1958, The BART District buys the Northwestern Pacific Railroad from the Southern Pacific for use in the BART system
• 1960, The Pennsylvania Railroad begins limited operation of the BART system
• 1967, The Pennsylvania Railroad inaugurates the final link in the BART system with completion of electrification to Cloverdale
• 1967, The Pennsylvania Lines' merger with the New York Central is approved, on condition that the New York Central first divest iteslf of several holdings so as not to unduely stifle competion
• 1968, The Colorado and Southern Railroad funds construction of Keystone ski resort in Colorado under a new Pennsylvania Railroad Corporation subsidiary, Keystone Recreation
• 1970, The New York Central divests itself of the Boston & Albany Railroad, which begins independent operation
• 1972, The New York Central consolidates the Cleveland, Cincinnati, Chicago, & St. Louis Railroad and the Michigan Central Railroad into the Buffalo, Chicago, and St. Louis Railroad. Attempts to sell the line are unsuccessful
• 1975, The Empire Corridor electrification project is completed
• 1976, The Federal Government creates the Consolidated Rail Corporation, which assumes control of the Buffalo, Chicago, and St. Louis Railroad (along with several other railroads) and several branch lines in Pennsylvania, New York, and Ohio, completing the Pennsylvania Railroad Corporation's obligations related to the merger the New York Central
• 1980, The Staggers Rail Act passes, deregulating the railroad industry
• 1981, The Kansas Pacific Railway and St. Louis, Iron Mountain, and Southern Railroad are consolidated into the Pennsylvania Lines, and The Denver and Rio Grande Western Railroad and Texas and Pacific Railroad are consolidated into the Colorado and Southern Railroad
• 1982, The Sacramento Northern Railroad, Tidewater Southern Railroad, and other Western Pacific subsidiaries are consolidated into the Western Pacific Railroad
• 1984, The New York Central is consolidated into the Pennsylvania Lines, and electrification is begun on the former New York Central Water Level Route from New York City to Buffalo, NY
• 1985, The Pennsylvania Railroad Corporation purchases a controlling interest in the Lehigh Valley Railroad from the Consolidated Rail Corporation, and it is consolidated into the Pennsylvania Lines
• 1987, The Southern Pacific Santa Fe merger is denied. The Pennsylvania Railroad Corporation agrees to buy the former Southern Pacific physical plant and assets, but the purchase is denied by the Federal Government. Eventually, the purchase is split between the Western Pacific Railroad, which gains contol of the coastal route from Los Angeles to San Francisco and the southern route from Los Angeles to El Paso, Texas, and the Union Pacific Railroad, which gains control of the balance of the former Southern Pacific
• 1988, The Pennsylvania Railraod Corporation buys a controlling interest in the New York, New Haven, and Hartford railroad from the Consolidated Rail Corporation
• 1989, The St. Louis, Iron Mountain, and Southern Railroad and the Texas and Pacific Railroad are consolidated into the Colorado and Southern Railroad
• 1992, Upgrades begin to several sections of the network in preparation for high speed rail service, including an extension from Los Angeles to San Diego
• 1994, The Capital Corridor, Keystone Corridor, and Empire Corridor infrastructure upgrades are completed and ACELA high speed rail service begins between Buffalo, Boston, New York, Pittsburgh, and Washington DC. Early production and performance problems with the ACELA trainsets and improved rail lead to major redesigns and grade seaparations in other high-speed markets
• 1999, The New York, New Haven, and Hartford railroad is consolidated into the Pennsylvania Rail Lines
• 2003, The California Corridor infrastructure upgrades are completed. High speed rail service begins between Sacramento, San Francisco, Los Angeles, and San Diego
• 2004, The Gulf Corridor infrastructure upgrades are completed and high speed rail service begins between Houston, Dallas, and New Orleans using JetTrain technology
• 2010, Using American Reinvestment and Recovery Act funding, work begins on preparations for high speed service along the I25 corridor from Cheyanne, WY to Trinidad, CO
• 2014, The Pennsylvania Railroad invests in the private effort to build a new PRR class T1 steam locomotive.