The decision to construct an immersed tube tunnel bypass followed an extensive public consultation, named the Collcon Feasibility Study. This ruled out another bridge by the castle on aesthetic grounds, since it would have damaged the view of the world heritage site Conwy Castle, and the two bridges by Robert Stephenson and Thomas Telford. Another alternative bridge crossing was proposed at Deganwy, but this too was ruled out for aesthetic reasons. An inland alternative with heavy grades which would have passed over Bwlch y Ddeufaen pass at , following the old Roman road, was also worked up but rejected for cost and utility reasons.