In August 1956 GM Coach produced an experimental air-conditioned 96" wide TDH-5106 bus, it was placed in service by Fifth Avenue Coach Lines as No. 3100 and was purchased in 1958. This coach served as the prototype for the longitudinal, U-shaped seating to the rear of the manually operated exit door yielding 45 seats. This floor plan and doors were retained on the remaining TDH-5106s and TDH-5301s. This coach is now part of the Authority's historic fleet.