Chief Minister Alf Cannan asked his former DoI minister to quit over the 20mph rollout and issues with local authorities.
The government has released the letter Mr Cannan sent to Dr Michelle Haywood outlining why a change was needed.
He said this was necessary to allow government to “pursue a renewed approach to a number of infrastructure matters that you are currently leading”.
Mr Cannan added: “In particular, the position of the DOI in interpreting the rollout of 20mph roads together with the controversy regarding the Local Government Bill are matters that I now wish to see addressed differently.”
He went on to thank Dr Haywood for her work over the past 15 months and “the work that you have done to restore ATC operations and improve governance”.
Dr Haywood successor Tim Crookall has said he will put a pause on the rollout of new 20mph zones which was due to begin this week.