The "Dorsey" in question appears to be Ralph T. Dorsey, city traffic chief....
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1920's
He gave us the world's greatest pacifier, otherwise known as the pedestrian push-button signal.....a mini-bio from here:
https://ladot.lacity.org/sites/defau...fornia.pdf ......
Ralph T. Dorsey was the first Traffic Engineer for the City of Los Angeles and a colorful and remarkable person. He was born in Downtown Los Angeles and received a high school education. He was the nephew of Susan Miller Dorsey after whom the high school in Los Angeles is named. He was a short, wiry man who became a semi-pro baseball player, a flyweight boxer, a miner and finally, an electrician, a trade that he learned from correspondence school. He was employed as an electrician with the City of Los Angeles when the first experiments with automated traffic signals were underway.
He was the inspector of the initial signal system of 31 intersections in Downtown Los Angeles. In this capacity he not only became an expert in the operation of traffic signals, but more importantly in the operation of traffic through signal timing techniques. The roots of traffic engineering lie in the art of safe and efficient intersectional traffic operation. Dorsey epitomized that art by being the first person to successfully control pedestrians, operate an interconnected signal system (with a control center), develop optimum signal system offsets, and develop 16 daily timing plans all by 1926. In 1928 he pioneered reverse lane operation, and in one case, 12th Street was operated as a reversible one-way street. Also, in1928 he applied the first known railroad pre-emption features. He installed the first known pedestrian push button signal in January 1929.
He had the longest tenure as the City’s top transportation official. From June 1930 until his retirement in 1954 he headed the Bureau of Street Traffic Engineering, the Department of Street Traffic Engineering, the Department of Traffic Engineering and the Department of Traffic. He indeed was a pioneer, an innovator, a character and one who invented ways to keep traffic flowing long before there were standard practices.