The Hartford and New Haven Railroad's lines were merged into Penn Central Transportation Company with the rest of the bankrupt New Haven Railroad at the end of 1968; Penn Central itself went bankrupt and was merged into government-formed Conrail in 1976.

[1] Alexander Catlin Twining was commissioned to survey the railroad's route, originally intended to pass through Middletown, Connecticut.

However, Twining decided during his survey that building through the hilly terrain around Middletown would be too difficult, and instead chose an alignment further west, via Meriden, Connecticut.

[1] The citizens of Middletown were unhappy about being bypassed, but they would have to wait for more than a decade before a branch line reached their city.

[3] With the railroad's two namesake cities now connected, the company turned its attention northward to Springfield, Massachusetts.

In that city, the Hartford and New Haven would be able to connect with the Western Railroad, which was building its own line from Boston to Springfield.

The new railroad company never operated independently, as it was simply a vehicle for the Hartford and New Haven to extend its line into Massachusetts.

National passenger rail carrier Amtrak, formed in 1971, purchased the Hartford and New Haven route outright in 1976, becoming its New Haven–Springfield Line.

[1] By the mid to late 2000s, Connecticut and Massachusetts were both advocating for improvements and expansion of commuter service on the line, at that point consisting solely of Amtrak's New Haven-Springfield Shuttle, offering six trains each direction daily.

[8] In total, four branches were built off of the main line by other companies, all of which were quickly acquired by the Hartford and New Haven after completion.

[9] This short railroad contracted out train operations to the Hartford and New Haven, before the latter company purchased it outright in 1868.

Upon the completion of construction and the railroad's opening on December 12, 1870, it was operated by the Hartford and New Haven, and was formally merged into that company in 1871.