Today, it takes 45 or so minutes to drive between Borås and Göteborg on Riksväg 40. Considering that Borås was a sizeable town by 1700, it makes me wonder what the path between Göteborg and Borås looked like during the 18th century. Were there several "roads" between the two cities? Did they go through other settlements (like Bollebygd)? How long did it take to reach Göteborg from Borås? Are there any contemporary accounts of travelling on this path?
While I'm not an expert on Västra Götaland, just looking at a map will show a fairly obvious candidate for the older road, namely road Länsväg 156. First, it's named "Göteborgsvägen" at the point where it exits Borås, indicating it must have been a main route to Göteborg. Other than that, it has all the typical characteristics I know of older roads (and not just in Sweden): It takes a much longer route than the modern main road Rv40, and passes through many more villages/settlements on the way. Also, the railroad follows it more closely, which is often the case, since the railroads often predate automotive transport and needed to service all the small villages the road did. (in this case, the railroad was inaugurated in 1894)
Rv40 on the other hand is typical of modern roads; it bypasses the settlements and takes a straighter route. In part because technology allowed the building of straighter roads through difficult terrain, and in part because you no longer want heavy traffic going through the middle of settlements if it can be avoided.
(Road 156 turns south at Härryda though, where the route to Göteborg is continued by Härrydavägen instead, which merges with the current stretch of Rv40 around Landvetter, so the final bit is the same for both routes)
Now, to back up that conjecture with some hard facts: If I'm right, there should be at least a few old milestones (and other old stuff) along road 156 and no significant amount around Rv40.
Checking with Riksantikvarieämbetets database (one of Sweden's most entertaining websites for any history interested person), you'll quickly find that that's the case. For instance, there's a milestone from 1765 in Bollebygd and one from 1771 in Sandared and another a few km east of Landvetter airport, all along road 156. While there's not much along road Rv40, and much of the stuff that is marked there are archaeological finds, perhaps unearthed when the road was built.
So it seems quite certain Länsväg 156 was the main road during that time period. Possibly with some minor deviations from its current route.
