Finding the traces of old main roads: the A10

Coming back from Hatfield to Cambridge, we discovered there is one road, the A10, that goes all the way. Today that road is broken into stretches of dual carriageway, and sometimes diverges from the older road, but it was possible to retrace the course of the original A10 during an hour or two. Our perspective was not to go anywhere very fast but to see the towns on the old road. Clearly towns such as Ware, Buntingford were old coaching stations.

That led to a further thought: the A10 was clearly a major route as far back as the 16th-17th centuries, to judge from the buildings beside the road that looked like they had been inns. So when were the road numbers introduced? And what were they based on?

Buntingford, a town of just a few thousand people, has coaching inns; it makes you remember the lovely big coaching inns at Benson, Oxfordshire, a town completely bypassed, but which (presumably) was an important stop between London and Oxford. I have a photo of a coaching inn from Godalming, Surrey (shown below), though sadly nothing from the old A10 road as yet. 

Answers

Wikipedia tells us road numbers were introduced from 1913 - but these were obviously based on the main routes existing at the time. Why then is there an Old North Road, as well as a Great North Road? When did it change from one to the other?

What about the A10?

This was the London to Kings Lynn main road, while the A11 was London to Norwich, and the A12 London to Great Yarmouth.

There is a Wikipedia entry for A10, which follows the former Ermine Street to Royston. However, this simply lists the history of bypasses and improvements. It appears largely to be derived from a website called SABRE (Society for All British Road Enthusiasts), written from the point of view of the motorist (“Ware is bypassed by a nice fast bit of new road”).

So is there any study of a particular road, going back before the numbered road system, and identifying what kind of travellers there were? One limitation of the Pevsner view of the world is that it is sliced up into places, with little consideration of how people would be travelling through those places.