A longer, double-truck version of the Birney car was developed in the 1920s, incorporating its most successful features. These were sold to a number of systems, including that of Tampa, Florida, and to the Texas Interurban Railway, which used them exclusively. In addition to 11 double-truck passenger cars, which featured deluxe interior appointments and toilets for interurban service, the Texas Interurban operated 3 unusual Birney-based double-truck express cars without passenger seats or windows– the only cars of this type ever built.