Carillion hefyd sydd wedi'i benodi gan Lywodraeth Cymru i ddylunio gwelliannau i gyffordd 15 a 16 o'r A55. Cyhoeddwyd rhybudd elw Carillion ym mis Gorffennaf 2017 ar ôl i gais y cwmni ar gyfer y prosiect ddod i law a'i asesu, ond cyn dyfarnu'r contract yn ffurfiol i'r cwmni.
Carillion are also the Welsh Government’s appointed contractor for the design of improvements to junction 15 and 16 of the A55. Carillion’s profit warning in July 2017 was released following the receipt and assessment of Carillion’s bid for the project, but prior to the formal award of the contract to Carillion.