The process was handled by the Crown Commercial Service and involved MediaCom, Mindshare, and MEC.
The account is said to be worth about £9 million. Carat has handled the media planning and buying account since 2002.
Matthew Hook, the managing director at Carat, said: "We are incredibly proud to continue our long-term relationship with the Department for Transport.
"We’re especially proud of their award-winning road safety programme, Think! and look forward to supporting them as they undertake their vital work."