Ridley, a fellow of the Royal Academy of Engineering, worked in the United States as a foundations design engineer and in the field of soil mechanics. He was a site engineer for the construction of Bradwell nuclear power station and a design engineer for the Nuclear Power Group of Knutsford. Ridley was later chief research officer for the highways and transport department of the Greater London Council before he was selected, in 1969, to become the director-general of the newly founded Tyne & WearPassenger Transport Executive. At the time of his appointment the chairman of Newcastle City Council's traffic and transport committee stated "He is a very brainy backroom boy, well versed in the theory of transport. It will be interesting to see how he deals with the management of a very large transport undertaking as he has had no management experience whatever, or experience of financial control. We wish him well, however". Ridley remained in post as director general until 1975 when he was appointed managing director of the Hong KongMass Transit Railway Corporation. Ridley left Hong Kong in 1978 and during the 1980s was chief executive officer of London Underground. In the 1986 New Year Honours he was appointed a Commander of the Order of the British Empire. In 1987 Ridley won the Institution Prize of the Chartered Institution of Highways and Transportation. He was appointed a director of the Chartered Institute of Logistics & Transport in 1991, serving in that role until 1993 and for a later stint between 1999 and 2001. He was a director of Halcrow Fox consulting engineers between 1992 and 2004, of the Major Projects Association between 1995 and 2009 and of the RAC Foundation from 1995 to 2010.
Institution of Civil Engineers
Ridley served as president of the Institution of Civil Engineers from March 1995 to November 1996. He was appointed to the presidency following the death in office of Edmund Hambly. Ridley served out the remainder of Hambly's term as well as the usual 12 months in office, becoming the first person to do so since Herbert Manzoni in 1961. In June 1995 he called an extraordinary meeting of the ICE Council at its One Great George Street headquarters to discuss the future of the loss-making New Civil Engineer magazine. The ICE, facing a £4 million overdraft from a renovation of the headquarters, and the slide of the magazine into unprofitability was considering selling the publishing arm. The council met in a closed session for the first time in its history, with the room being cleared of all observers and the secretariat leaving only the voting members. The sale of New Civil Engineer and the institution's specialist engineering magazines to Emap was agreed later that month - though the ICE retained control of its book and journal publications.