As with just about any other Northern Ireland motorway, the M5 was destined for something bigger. It takes four of the M2's ten lanes on the way out of Belfast and then, as if it's not sure what to do without the other six, gives up a mile or so later and stops on a roundabout with the A2.
This road was meant to go all the way to Carrickfergus - but, of course, never did. When Westminster took direct control of Northern Ireland in the early 1970s, all the plans that hadn't yet been started were instantly frozen, and have remained so ever since. The M5 was lucky in that it remained in the roads programme; or rather, a short stub of it did, linking the M2 to the A2 along the shoreline. The motorway opened in 1980, but it's little more than a hint at what was once planned.
Impressively, almost the whole of the M5 is built on land reclaimed from the sea, and for most of its length runs on a causeway between open water and a man-made lagoon.
Onwards from the end of the road, there's no prospect of the M5 towards Carrickfergus or the once-planned M6 into Newtownards being built now. The land set aside for them has been partly built on, and in recent years the A2 has been widened to provide a dual carriageway, a simpler and cheaper way of doing the job the M5 was designed for.