The R110A and R110B were prototype subway cars built in the early 1990s for the New York City Transit Authority (NYCTA) as part of the Program for Action to test modern subway technologies. These experimental trains were developed to evaluate new design elements for future fleets, leading to the R142 and R143 series. The **R110A**, built by Kawasaki Heavy Industries in 1992, was a ten-car set designed for the A Division (IRT). Its distinctive stainless steel body has a futuristic, streamlined look. The R110A also had wider doors, digital signage, and a modernized propulsion system. However, due to mechanical and reliability issues, it was retired in 1999. The **R110B**, built by Bombardier Transportation in 1992, was a five-car set intended for the B Division (IND/BMT). Its design was entirely different from that of the R110A, with full-width cabs and an open-gangway-style layout for easy passenger movement. The R110 B also faced operational challenges and was retired in 2000. Though short-lived, the R110A and R110B directly influenced the design of later New York City subway cars, including the R142, R143, and subsequent models, by testing features such as electronic signage, advanced propulsion, and improved accessibility.