Simon Calder: Tracked down - Britain's greatest A-road. Or is it?

The man who pays his way

Two weeks ago, I was rescued by les pompiers, though not in the customary circumstances. I was seeking to descend from Les Arcs in the French Alps. Warning signs strictly prohibited pedestrians from walking down the D119 because of the risk of avalanches. So I hitched, and the local firefighters stopped – immediately improving my hitch-hiking poker hand. All I need to complete an emergency services trilogy is a lift in an ambulance, with or without patient.

The D119 was the last road I hitch-hiked along; the first was a less scenic highway, the A264 between East Grinstead and Crawley. I happened to be born beside the A23 just a few yards from where it crossed the A264, and these two A-roads formed the basis for all my early travel experiences. This week, the architectural worth of the British petrol station has been celebrated – and on pages 8 and 9 we feature the "highway to the sun", the A303 through the west of England, and the travel memories it unlocks.

A-roads are far more part of the nation's travel patchwork than are motorways. There are more of them; they thread through, or go to, all the best places in Britain from Land's End (A30) to John O'Groats (A9); and they were designed for an gentler age of slower travel (though it must be said, a time of much higher accident rates).

While the UK may lack a "mother road" to match Route 66 or the Great Ocean Road, it has some excellent candidates for the nation's prime artery. The greatest is the A5, which starts beside a branch of Snappy Snaps at Marble Arch in central London and ends untidily at the port of Holyhead, on the island that is even more detached from mainland Britain than is Anglesey.

The A5's achievements during its 260-mile meander are remarkable. From its southern start the road acts as the main artery for the Arabic community in London; mutates into a suburban high street (Kilburn, Cricklewood); provides an escape route at either end of Milton Keynes; delivers optimistic punters to Towcester racecourse, and leads most of them sorrowfully home.

Before the M6 and the M6 Toll, the A5 was the main road connecting the South-east with the North-west, carving a graceful arc above the clutter of the West Midlands. It skirmishes with the A41, a lesser highway that also begins at Marble Arch but fizzles out in Birkenhead; they tussle on the way out of London and once again at a lonely roundabout outside Weston-under-Lizard in Staffordshire. Then the A5 traverses Shropshire, swerving around Shrewsbury. And that's just the "English" part of the A5, which follows the ancient course of the Roman Road known as Watling Street.

Trans-Cambrian driving force

Once across the River Ceiriog at Chirk and into Wales, Roman rigidity is replaced by Victorian engineering. Thomas Telford coaxed a highway to Holy Island through the spectacular terrain of North Wales, never allowing the gradient to exceed 1 in 20.

Near Llangollen, another Telford miracle appears, in the shape of a Unesco World Heritage Site: the Pontcysyllte Aqueduct, which bears narrowboats across the heavens. Then the A5 curls around the Horseshoe Falls and carves across the prettiest parts of Snowdonia, passing lonely chapels and nameless cairns.

Agreed, it's all downhill from here: the A55 muscles in on the action outside Bangor and relegates the A5 to a trans-Angleseyan afterthought. But shortly before this happens you can stop at the prettiest youth hostel in North Wales, Idwal Cottage. It stands beside the sharp northward turn at Llyn Ogwen – and happens to be where I intend to stay tonight, trains and boots willing. While I adore the A5, I have never actually driven along it.

Traffic news: it's the A595

Your nominations – and justifications – for other A-road contenders are warmly welcomed. To start you off, I sought the view of the Voice of Traffic, Sally Boazman of BBC Radio 2.

"The A595, which runs between Whitehaven and Barrow-in-Furness on the western edge of the Lake District. Stunning." Strangely, Ms Boazman also used to live beside the A23. But she never hitched along it.