ROMAG was developed from a wheeled system known as Monocab, originally designed by Edward Haltom and built to the extent of a test track by Vero Inc. in 1969.
Haltom noticed that the time to start and stop a conventional large monorail train, like those of the Wuppertal Schwebebahn, meant that a single line could only support between 20 and 40 vehicles an hour.
[1] Haltom turned his attention to developing a system that could operate with shorter timings, thereby allowing the individual cars to be smaller while preserving the same overall route capacity.
[1] Vero's test track opened shortly after the publication of the highly influential HUD reports that gave strong backing to the PRT concept.
They had already started work on a high-speed train under a 1970 Urban Mass Transit Administration (UMTA) contract, their Tracked Air-Cushion Vehicle (TACV) was a licensed version of the French Aérotrain.
[1] These changes eliminated the vast majority of the vehicle's moving parts, leaving only the doors and fans, and thereby offered dramatically increased reliability and reduced maintenance needs.
As the system did not depend on physical contact for traction, it would operate with equal effectiveness when covered with rain or snow, and could climb steeper grades and turn sharper corners.
[1] The ROMAG was one of four major PRT entries demonstrated at the Transpo 72 show at Dulles Airport in Washington, DC, but as the maglev version had only just been set up in California, Rohr used the older wheeled system from Vero instead.
[1][4] In the aftermath of the show, the UMTA started the Advanced Group Rapid Transit (AGRT) program to continue development funding for three of the systems, Boeing, Otis and Rohr.