During the initial design programme for the extension of the M1 motorway, the National Roads Authority approached Iarnród Éireann in 1997 and asked them to carry out a feasibility study of a possible overbridge crossing of the new road about two miles north of Dundalk. The site of the proposed crossing is about half a mile west of the intersection of the original N1 Dublin to Belfast road with the R173 Ballymascanlon to Carlingford road at milepost 56³/₄.

A number of different types of construction were examined bearing in mind that a long-term interruption of rail services was not an acceptable option to Iarnród Éireann. The first one would be a traditional, in-situ bridge, which would involve either a temporary or permanent diversion of the railway line. The second was an off site constructed deck with in-situ support piers constructed under the existing line while traffic was allowed to continue. Lastly another proposal was to use the JMB Methodes patented bridge construction system, which involved the building of a monolithic concrete deck, support piers and raft foundation structure adjacent to the eventual bridge site and sliding it into place during a short possession. The outcome of the study was that the last mentioned method was considered to be the most suitable from a cost and operational point of view and was, therefore, selected as the preferred option.

The construction system involved was devised by one Jean-Marie Beauthier, a French engineer, in 1992 and patented by him using his company, JMB Methodes. The idea was devised particularly for the replacement of existing railway under bridges or new bridges, which were required to cross projected roads. The name given to the system was ‘Autoripage’ and it had been used on a significant number of projects prior to the Dundalk Western By-Pass. Messrs. VSL, which is a large international French contracting company seem to have been involved in most of the earliest projects on the continent, with an English company Messrs. Osbornes being appointed for those in the UK. The bridge at Dundalk was, at 7,500 tonnes, the largest up to that date but this has since been surpassed in August of this year by one at Boissy, Ile-de-France, for RER line A, which weighed in at 12,500 tonnes. Another example was recently completed at Shortlands Junction in southeast London also in August of this year but this one was only 4500 tonnes. It was, however, interesting in so far as it involved two railway lines.

A bridge agreement was finalised in October 2003 between Iarnród Éireann, the National Roads Authority and Louth County Council setting out the legal conditions for allowing the bridge to be constructed on railway property. This, in turn, involved an agreement for the design and construction of the new bridge between the NRA and Celtic Roads Group Ltd., who were the Public Private Partnership company. The main contractor was Dundalk Joint Venture and their sub-contractors consisted of design consultants, Mott McDonald EPO together with the patent holder, JMB Methodes and their construction sub contractor, VSL as well as the earth moving sub contractor, Logan Earth Moving Ltd. Iarnród Éireann were supported by Roughan & O’Donovan (structural), AGEC (geotechnical) and Geoffrey Osbournes Ltd (Autoripage system). The design was completed in July 2004. Work commenced on site in November 2004, with the possession scheduled for the Easter weekend in March 2005. This was an ambitious schedule considering the time of year and the complexity of the work to be undertaken.