@louis A combination of factors, but primarily roads. You have to remember road building is about the building of the path itself, that isnt the most impactful part usual. The biggest impact comes from the bridge building.
That said paving roads (even with rocks) generally does mean faster travel with fewer break downs. So there is likely an effect there too. It isnt exactly minor.
Have you ever tried to travel through the woods without following a trail, particularly if its overgrown? Good luck.
@louis You have different levels of roads.. a walked path will of course form that you dont need to bushwack, but this isnt always consistent. Plus dirt roads dont really help with speed or breakdown completely as there will be lots of holes, puddles, rivers and large fallen trees in your way. A natural path vs a maintained road (even a basic one) can easily double your travel speed if i had to guess.
I am sure map and knowledge played a noticeable role too. It would be interesting to be able to actually quantify it somehow.
Keep in mind though during this period bridge building was huge.. every settlement made the building of bridges one of its top priorities. Typically it was forced labour where all settlers needed to contribute to bridge building or else be fined.
@freemo Well, sure, but even the roads back then usually formed along natural wildlife trails.
I wonder how much of the gain in speed was simply knowledge. Better maps, better managed expectations, more trail experience, etc.