An aeronautical engineer by training, Dr Mitchell worked at the Road Research Laboratory/Transport and Road Research Laboratory/Transport Research Laboratory from 1970 to 1994, focusing on public transport, transport planning and the social effects of transport policies.
From 1982 he was Head of the Environment Divison. From the early 1980s he also ran TRRL’s research on transport for disabled people and led the group that drafted the first DPTAC specification for local buses in 1988.
He co-chaired the US Transportation Research Board Committee on Accessible Transportation and Mobility 2003-09 and is an Emeritus Member of TRB. In 2010 he produced a review of research on older drivers for the RAC Foundation, and also worked for the UN Development Programme in Malaysia advising on ways to improve public transport for older and disabled people.
He was a member of the Road Safety Foundation’s Older Driver Task Force which reported in 2016, leading the Working Group that provided evidence to support the work of the Task Force. He also serves on the Hampshire Older Driver Forum, which coordinates police and road safety activities to support older drivers.