Belfast to Dungannon
Completed in the 1960s and not changed much since, the Northern Ireland M1 is a mostly two-lane affair that stretches to nearly 40 miles - the longest stretch of road of this standard in the province.
One hard shoulder's enough for one carriageway, right? Well...not according to one long-lost design standard.
It was the UK's only single-carriageway motorway, and twenty years ago it ceased to exist. This is the story of the strange fascination it held, and of my place in history.
The second part of the story, where we learn why exactly the M4 gets narrower on the final approach to Europe’s biggest city.
The M4 into London was one of the UK's earliest and most ambitious motorway projects. It was bold, pioneering... and almost instantly regretted.
How do you describe a road? One way is to use these engineering abbreviations, much loved by the UK's community of road enthusiasts.
