Transport Scotland chief executive Malcolm Reed announced this week that he will retire in the New Year.
The executive agency confirmed that Reed will take leave in February but as yet no replacement has been announced. Dr Reed, 64, joined the organisation prior to its creation in January 2006.
Reed said: "It has been a tremendous privilege for me to lead the setting up of Transport Scotland and to steer the agency through its formative years.
“The transport infrastructure delivery programme, which is currently underway, is the largest for many decades. Over the last three years we have delivered the Stirling-Alloa-Kincardine rail project, the new Clackmannanshire Bridge and Dalkeith bypass, as well as managing the successful implementation of the national concessionary travel schemes and overseeing substantial increases in the demand for rail travel in Scotland.
“Work is also underway on major projects such the M74 completion, the Airdrie to Bathgate rail link as well as plans for the Glasgow Airport Rail link, electrification of the Edinburgh to Glasgow rail link and the Aberdeen Western Peripheral Route.
“While I will miss the excitement of being at the heart of transport delivery in Scotland, I feel the time is right to look to new challenges.”