The A1 runs from the M1 at Lisburn to the border at Newry and forms part of the main Belfast to Dublin road. Between the two ends of the A1 it passes three other towns - Hillsborough, Dromore and Banbridge. With the exception of the roundabout at the north end of Hillsborough all of these were built as ordinary T-junctions where vehicles have to cross the central reservation.

Due to the number of vehicles on this busy road (25,000 per day in 2005) and the high accident rate, the government has adopted a plan to grade separate all the major junctions on the route. Two were planned inititally - this one and the Rathfriland Road in Banbridge. A further four are in the pipeline at time of writing (July 2006). This one is what the Roads Service term a "compact grade separated junction" – it does not have full length sliproads and the curves are quite tight.

The scheme saw the road dug up in stages to install a new underpass and then the laying of a new link road beneath the A1 and two spurs to link to each carriageway of the A1. The opportunity was also taken to resurface a mile of the A1. The scheme was originally proposed in the late 1990s but was delayed for years because of land aquisition problems and the need for a public inquiry.