in 1924, what is now NY 434 was designated as part of NY 17, a cross-state highway connecting Erie, Pennsylvania, to New York City. In the mid-1960s, construction began on the portion of the Southern Tier Expressway (STE) between the village of Owego and the city of Binghamton. The segment from Owego to Johnson City was completed and opened to traffic in 1969, with the portion from Owego to Vestal becoming a realignment of NY 17. NYSDOT initially designated the former routing of NY 17 from Owego to NY 26 in Vestal as NY 188. However, on October 10, 1969, NYSDOT announced that they had elected to designate the highway as NY 434 instead, even though signage for NY 188 had already been erected. The state cited potential confusion between NY 188 and the proposed I-88 northeast of Binghamton as its reason for the change. At the same time, NYSDOT stated that the NY 434 designation would only extend as far west as the Tioga–Broome County line even though NY 188 had continued to Owego. Instead, the state planned on transferring ownership and maintenance of former NY 17 from Owego east to the county line to Tioga County. This transaction was completed on November 24, 1969. Designation and extensions NY 434 was officially assigned on January 1, 1970, as part of a wide-scale update of NYSDOT's Official Description of Touring Routes in New York State. A list of changes accompanying the log described NY 434 as "a new number assigned to replace former NY 17 between the Broome–Tioga County line and NY 26 in Vestal." At the time, NY 434 also ended at NY 17 in Vestal. Although the STE was open from Vestal to Johnson City, it was not slated to become part of NY 17 until the segment of the STE from Johnson City to Interstate 81 was completed. As a result, NY 17 exited the STE at Vestal, overlapped NY 26 south to Vestal Parkway, and followed its original alignment along Vestal Parkway into downtown Binghamton. The Johnson City–I-81 piece of the expressway was completed and opened to traffic by 1973. NY 17 was realigned to follow the STE while NY 17's former routing from Vestal to Binghamton became an extension of NY 434 on July 1, 1974. Like the NY 17 realignment, the NY 434 extension had been planned years before. The former routing of NY