Northern Ireland's road transport regulator Donald Armstrong is to step down from the role at the end of March.
Career civil servant Armstrong oversaw the introduction the new Transport Regulation Unit (TRU) in the province four years ago and became its head.
The unit - which became operational in July 2012 - has succeeded in registering and bringing more than 4,000 own account operators in Northern Ireland into the O-licensing system.
Previously, only hire or reward operators in Northern Ireland were required to have an O-licence.
It has also held a series of public inquiries, one of the most notable involving the revocation of the licence of Craigavon-based Dewart Transport last May following boss Richard Dewart's conviction for forgery relating to tachograph records.
Armstrong told Motortransport.co.uk: "I am stepping down to enjoy a more relaxed pace of life and to focus on other interests.
"My successor is in the process of being appointed and no doubt news on that will be available in the next few weeks."
